[linux-2.6] / fs / ext4 / inode.c

/*
 *  linux/fs/ext4/inode.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card (card@masi.ibp.fr)
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/inode.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Goal-directed block allocation by Stephen Tweedie
 *      (sct@redhat.com), 1993, 1998
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller (davem@caip.rutgers.edu), 1995
 *  64-bit file support on 64-bit platforms by Jakub Jelinek
 *      (jj@sunsite.ms.mff.cuni.cz)
 *
 *  Assorted race fixes, rewrite of ext4_get_block() by Al Viro, 2000
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/time.h>
#include <linux/jbd2.h>
#include <linux/highuid.h>
#include <linux/pagemap.h>
#include <linux/quotaops.h>
#include <linux/string.h>
#include <linux/buffer_head.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/mpage.h>
#include <linux/uio.h>
#include <linux/bio.h>
#include "ext4_jbd2.h"
#include "xattr.h"
#include "acl.h"
#include "ext4_extents.h"

#define MPAGE_DA_EXTENT_TAIL 0x01

static inline int ext4_begin_ordered_truncate(struct inode *inode,
                                              loff_t new_size)
{
        return jbd2_journal_begin_ordered_truncate(&EXT4_I(inode)->jinode,
                                                   new_size);
}

static void ext4_invalidatepage(struct page *page, unsigned long offset);

/*
 * Test whether an inode is a fast symlink.
 */
static int ext4_inode_is_fast_symlink(struct inode *inode)
{
        int ea_blocks = EXT4_I(inode)->i_file_acl ?
                (inode->i_sb->s_blocksize >> 9) : 0;

        return (S_ISLNK(inode->i_mode) && inode->i_blocks - ea_blocks == 0);
}

/*
 * The ext4 forget function must perform a revoke if we are freeing data
 * which has been journaled.  Metadata (eg. indirect blocks) must be
 * revoked in all cases.
 *
 * "bh" may be NULL: a metadata block may have been freed from memory
 * but there may still be a record of it in the journal, and that record
 * still needs to be revoked.
 */
int ext4_forget(handle_t *handle, int is_metadata, struct inode *inode,
                        struct buffer_head *bh, ext4_fsblk_t blocknr)
{
        int err;

        might_sleep();

        BUFFER_TRACE(bh, "enter");

        jbd_debug(4, "forgetting bh %p: is_metadata = %d, mode %o, "
                  "data mode %lx\n",
                  bh, is_metadata, inode->i_mode,
                  test_opt(inode->i_sb, DATA_FLAGS));

        /* Never use the revoke function if we are doing full data
         * journaling: there is no need to, and a V1 superblock won't
         * support it.  Otherwise, only skip the revoke on un-journaled
         * data blocks. */

        if (test_opt(inode->i_sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA ||
            (!is_metadata && !ext4_should_journal_data(inode))) {
                if (bh) {
                        BUFFER_TRACE(bh, "call jbd2_journal_forget");
                        return ext4_journal_forget(handle, bh);
                }
                return 0;
        }

        /*
         * data!=journal && (is_metadata || should_journal_data(inode))
         */
        BUFFER_TRACE(bh, "call ext4_journal_revoke");
        err = ext4_journal_revoke(handle, blocknr, bh);
        if (err)
                ext4_abort(inode->i_sb, __func__,
                           "error %d when attempting revoke", err);
        BUFFER_TRACE(bh, "exit");
        return err;
}

/*
 * Work out how many blocks we need to proceed with the next chunk of a
 * truncate transaction.
 */
static unsigned long blocks_for_truncate(struct inode *inode)
{
        ext4_lblk_t needed;

        needed = inode->i_blocks >> (inode->i_sb->s_blocksize_bits - 9);

        /* Give ourselves just enough room to cope with inodes in which
         * i_blocks is corrupt: we've seen disk corruptions in the past
         * which resulted in random data in an inode which looked enough
         * like a regular file for ext4 to try to delete it.  Things
         * will go a bit crazy if that happens, but at least we should
         * try not to panic the whole kernel. */
        if (needed < 2)
                needed = 2;

        /* But we need to bound the transaction so we don't overflow the
         * journal. */
        if (needed > EXT4_MAX_TRANS_DATA)
                needed = EXT4_MAX_TRANS_DATA;

        return EXT4_DATA_TRANS_BLOCKS(inode->i_sb) + needed;
}

/*
 * Truncate transactions can be complex and absolutely huge.  So we need to
 * be able to restart the transaction at a conventient checkpoint to make
 * sure we don't overflow the journal.
 *
 * start_transaction gets us a new handle for a truncate transaction,
 * and extend_transaction tries to extend the existing one a bit.  If
 * extend fails, we need to propagate the failure up and restart the
 * transaction in the top-level truncate loop. --sct
 */
static handle_t *start_transaction(struct inode *inode)
{
        handle_t *result;

        result = ext4_journal_start(inode, blocks_for_truncate(inode));
        if (!IS_ERR(result))
                return result;

        ext4_std_error(inode->i_sb, PTR_ERR(result));
        return result;
}

/*
 * Try to extend this transaction for the purposes of truncation.
 *
 * Returns 0 if we managed to create more room.  If we can't create more
 * room, and the transaction must be restarted we return 1.
 */
static int try_to_extend_transaction(handle_t *handle, struct inode *inode)
{
        if (handle->h_buffer_credits > EXT4_RESERVE_TRANS_BLOCKS)
                return 0;
        if (!ext4_journal_extend(handle, blocks_for_truncate(inode)))
                return 0;
        return 1;
}

/*
 * Restart the transaction associated with *handle.  This does a commit,
 * so before we call here everything must be consistently dirtied against
 * this transaction.
 */
static int ext4_journal_test_restart(handle_t *handle, struct inode *inode)
{
        jbd_debug(2, "restarting handle %p\n", handle);
        return ext4_journal_restart(handle, blocks_for_truncate(inode));
}

/*
 * Called at the last iput() if i_nlink is zero.
 */
void ext4_delete_inode (struct inode * inode)
{
        handle_t *handle;
        int err;

        if (ext4_should_order_data(inode))
                ext4_begin_ordered_truncate(inode, 0);
        truncate_inode_pages(&inode->i_data, 0);

        if (is_bad_inode(inode))
                goto no_delete;

        handle = ext4_journal_start(inode, blocks_for_truncate(inode)+3);
        if (IS_ERR(handle)) {
                ext4_std_error(inode->i_sb, PTR_ERR(handle));
                /*
                 * If we're going to skip the normal cleanup, we still need to
                 * make sure that the in-core orphan linked list is properly
                 * cleaned up.
                 */
                ext4_orphan_del(NULL, inode);
                goto no_delete;
        }

        if (IS_SYNC(inode))
                handle->h_sync = 1;
        inode->i_size = 0;
        err = ext4_mark_inode_dirty(handle, inode);
        if (err) {
                ext4_warning(inode->i_sb, __func__,
                             "couldn't mark inode dirty (err %d)", err);
                goto stop_handle;
        }
        if (inode->i_blocks)
                ext4_truncate(inode);

        /*
         * ext4_ext_truncate() doesn't reserve any slop when it
         * restarts journal transactions; therefore there may not be
         * enough credits left in the handle to remove the inode from
         * the orphan list and set the dtime field.
         */
        if (handle->h_buffer_credits < 3) {
                err = ext4_journal_extend(handle, 3);
                if (err > 0)
                        err = ext4_journal_restart(handle, 3);
                if (err != 0) {
                        ext4_warning(inode->i_sb, __func__,
                                     "couldn't extend journal (err %d)", err);
                stop_handle:
                        ext4_journal_stop(handle);
                        goto no_delete;
                }
        }

        /*
         * Kill off the orphan record which ext4_truncate created.
         * AKPM: I think this can be inside the above `if'.
         * Note that ext4_orphan_del() has to be able to cope with the
         * deletion of a non-existent orphan - this is because we don't
         * know if ext4_truncate() actually created an orphan record.
         * (Well, we could do this if we need to, but heck - it works)
         */
        ext4_orphan_del(handle, inode);
        EXT4_I(inode)->i_dtime  = get_seconds();

        /*
         * One subtle ordering requirement: if anything has gone wrong
         * (transaction abort, IO errors, whatever), then we can still
         * do these next steps (the fs will already have been marked as
         * having errors), but we can't free the inode if the mark_dirty
         * fails.
         */
        if (ext4_mark_inode_dirty(handle, inode))
                /* If that failed, just do the required in-core inode clear. */
                clear_inode(inode);
        else
                ext4_free_inode(handle, inode);
        ext4_journal_stop(handle);
        return;
no_delete:
        clear_inode(inode);     /* We must guarantee clearing of inode... */
}

typedef struct {
        __le32  *p;
        __le32  key;
        struct buffer_head *bh;
} Indirect;

static inline void add_chain(Indirect *p, struct buffer_head *bh, __le32 *v)
{
        p->key = *(p->p = v);
        p->bh = bh;
}

/**
 *      ext4_block_to_path - parse the block number into array of offsets
 *      @inode: inode in question (we are only interested in its superblock)
 *      @i_block: block number to be parsed
 *      @offsets: array to store the offsets in
 *      @boundary: set this non-zero if the referred-to block is likely to be
 *             followed (on disk) by an indirect block.
 *
 *      To store the locations of file's data ext4 uses a data structure common
 *      for UNIX filesystems - tree of pointers anchored in the inode, with
 *      data blocks at leaves and indirect blocks in intermediate nodes.
 *      This function translates the block number into path in that tree -
 *      return value is the path length and @offsets[n] is the offset of
 *      pointer to (n+1)th node in the nth one. If @block is out of range
 *      (negative or too large) warning is printed and zero returned.
 *
 *      Note: function doesn't find node addresses, so no IO is needed. All
 *      we need to know is the capacity of indirect blocks (taken from the
 *      inode->i_sb).
 */

/*
 * Portability note: the last comparison (check that we fit into triple
 * indirect block) is spelled differently, because otherwise on an
 * architecture with 32-bit longs and 8Kb pages we might get into trouble
 * if our filesystem had 8Kb blocks. We might use long long, but that would
 * kill us on x86. Oh, well, at least the sign propagation does not matter -
 * i_block would have to be negative in the very beginning, so we would not
 * get there at all.
 */

static int ext4_block_to_path(struct inode *inode,
                        ext4_lblk_t i_block,
                        ext4_lblk_t offsets[4], int *boundary)
{
        int ptrs = EXT4_ADDR_PER_BLOCK(inode->i_sb);
        int ptrs_bits = EXT4_ADDR_PER_BLOCK_BITS(inode->i_sb);
        const long direct_blocks = EXT4_NDIR_BLOCKS,
                indirect_blocks = ptrs,
                double_blocks = (1 << (ptrs_bits * 2));
        int n = 0;
        int final = 0;

        if (i_block < 0) {
                ext4_warning (inode->i_sb, "ext4_block_to_path", "block < 0");
        } else if (i_block < direct_blocks) {
                offsets[n++] = i_block;
                final = direct_blocks;
        } else if ( (i_block -= direct_blocks) < indirect_blocks) {
                offsets[n++] = EXT4_IND_BLOCK;
                offsets[n++] = i_block;
                final = ptrs;
        } else if ((i_block -= indirect_blocks) < double_blocks) {
                offsets[n++] = EXT4_DIND_BLOCK;
                offsets[n++] = i_block >> ptrs_bits;
                offsets[n++] = i_block & (ptrs - 1);
                final = ptrs;
        } else if (((i_block -= double_blocks) >> (ptrs_bits * 2)) < ptrs) {
                offsets[n++] = EXT4_TIND_BLOCK;
                offsets[n++] = i_block >> (ptrs_bits * 2);
                offsets[n++] = (i_block >> ptrs_bits) & (ptrs - 1);
                offsets[n++] = i_block & (ptrs - 1);
                final = ptrs;
        } else {
                ext4_warning(inode->i_sb, "ext4_block_to_path",
                                "block %lu > max",
                                i_block + direct_blocks +
                                indirect_blocks + double_blocks);
        }
        if (boundary)
                *boundary = final - 1 - (i_block & (ptrs - 1));
        return n;
}

/**
 *      ext4_get_branch - read the chain of indirect blocks leading to data
 *      @inode: inode in question
 *      @depth: depth of the chain (1 - direct pointer, etc.)
 *      @offsets: offsets of pointers in inode/indirect blocks
 *      @chain: place to store the result
 *      @err: here we store the error value
 *
 *      Function fills the array of triples <key, p, bh> and returns %NULL
 *      if everything went OK or the pointer to the last filled triple
 *      (incomplete one) otherwise. Upon the return chain[i].key contains
 *      the number of (i+1)-th block in the chain (as it is stored in memory,
 *      i.e. little-endian 32-bit), chain[i].p contains the address of that
 *      number (it points into struct inode for i==0 and into the bh->b_data
 *      for i>0) and chain[i].bh points to the buffer_head of i-th indirect
 *      block for i>0 and NULL for i==0. In other words, it holds the block
 *      numbers of the chain, addresses they were taken from (and where we can
 *      verify that chain did not change) and buffer_heads hosting these
 *      numbers.
 *
 *      Function stops when it stumbles upon zero pointer (absent block)
 *              (pointer to last triple returned, *@err == 0)
 *      or when it gets an IO error reading an indirect block
 *              (ditto, *@err == -EIO)
 *      or when it reads all @depth-1 indirect blocks successfully and finds
 *      the whole chain, all way to the data (returns %NULL, *err == 0).
 *
 *      Need to be called with
 *      down_read(&EXT4_I(inode)->i_data_sem)
 */
static Indirect *ext4_get_branch(struct inode *inode, int depth,
                                 ext4_lblk_t  *offsets,
                                 Indirect chain[4], int *err)
{
        struct super_block *sb = inode->i_sb;
        Indirect *p = chain;
        struct buffer_head *bh;

        *err = 0;
        /* i_data is not going away, no lock needed */
        add_chain (chain, NULL, EXT4_I(inode)->i_data + *offsets);
        if (!p->key)
                goto no_block;
        while (--depth) {
                bh = sb_bread(sb, le32_to_cpu(p->key));
                if (!bh)
                        goto failure;
                add_chain(++p, bh, (__le32*)bh->b_data + *++offsets);
                /* Reader: end */
                if (!p->key)
                        goto no_block;
        }
        return NULL;

failure:
        *err = -EIO;
no_block:
        return p;
}

/**
 *      ext4_find_near - find a place for allocation with sufficient locality
 *      @inode: owner
 *      @ind: descriptor of indirect block.
 *
 *      This function returns the preferred place for block allocation.
 *      It is used when heuristic for sequential allocation fails.
 *      Rules are:
 *        + if there is a block to the left of our position - allocate near it.
 *        + if pointer will live in indirect block - allocate near that block.
 *        + if pointer will live in inode - allocate in the same
 *          cylinder group.
 *
 * In the latter case we colour the starting block by the callers PID to
 * prevent it from clashing with concurrent allocations for a different inode
 * in the same block group.   The PID is used here so that functionally related
 * files will be close-by on-disk.
 *
 *      Caller must make sure that @ind is valid and will stay that way.
 */
static ext4_fsblk_t ext4_find_near(struct inode *inode, Indirect *ind)
{
        struct ext4_inode_info *ei = EXT4_I(inode);
        __le32 *start = ind->bh ? (__le32*) ind->bh->b_data : ei->i_data;
        __le32 *p;
        ext4_fsblk_t bg_start;
        ext4_fsblk_t last_block;
        ext4_grpblk_t colour;

        /* Try to find previous block */
        for (p = ind->p - 1; p >= start; p--) {
                if (*p)
                        return le32_to_cpu(*p);
        }

        /* No such thing, so let's try location of indirect block */
        if (ind->bh)
                return ind->bh->b_blocknr;

        /*
         * It is going to be referred to from the inode itself? OK, just put it
         * into the same cylinder group then.
         */
        bg_start = ext4_group_first_block_no(inode->i_sb, ei->i_block_group);
        last_block = ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es) - 1;

        if (bg_start + EXT4_BLOCKS_PER_GROUP(inode->i_sb) <= last_block)
                colour = (current->pid % 16) *
                        (EXT4_BLOCKS_PER_GROUP(inode->i_sb) / 16);
        else
                colour = (current->pid % 16) * ((last_block - bg_start) / 16);
        return bg_start + colour;
}

/**
 *      ext4_find_goal - find a preferred place for allocation.
 *      @inode: owner
 *      @block:  block we want
 *      @partial: pointer to the last triple within a chain
 *
 *      Normally this function find the preferred place for block allocation,
 *      returns it.
 */
static ext4_fsblk_t ext4_find_goal(struct inode *inode, ext4_lblk_t block,
                Indirect *partial)
{
        struct ext4_block_alloc_info *block_i;

        block_i =  EXT4_I(inode)->i_block_alloc_info;

        /*
         * try the heuristic for sequential allocation,
         * failing that at least try to get decent locality.
         */
        if (block_i && (block == block_i->last_alloc_logical_block + 1)
                && (block_i->last_alloc_physical_block != 0)) {
                return block_i->last_alloc_physical_block + 1;
        }

        return ext4_find_near(inode, partial);
}

/**
 *      ext4_blks_to_allocate: Look up the block map and count the number
 *      of direct blocks need to be allocated for the given branch.
 *
 *      @branch: chain of indirect blocks
 *      @k: number of blocks need for indirect blocks
 *      @blks: number of data blocks to be mapped.
 *      @blocks_to_boundary:  the offset in the indirect block
 *
 *      return the total number of blocks to be allocate, including the
 *      direct and indirect blocks.
 */
static int ext4_blks_to_allocate(Indirect *branch, int k, unsigned long blks,
                int blocks_to_boundary)
{
        unsigned long count = 0;

        /*
         * Simple case, [t,d]Indirect block(s) has not allocated yet
         * then it's clear blocks on that path have not allocated
         */
        if (k > 0) {
                /* right now we don't handle cross boundary allocation */
                if (blks < blocks_to_boundary + 1)
                        count += blks;
                else
                        count += blocks_to_boundary + 1;
                return count;
        }

        count++;
        while (count < blks && count <= blocks_to_boundary &&
                le32_to_cpu(*(branch[0].p + count)) == 0) {
                count++;
        }
        return count;
}

/**
 *      ext4_alloc_blocks: multiple allocate blocks needed for a branch
 *      @indirect_blks: the number of blocks need to allocate for indirect
 *                      blocks
 *
 *      @new_blocks: on return it will store the new block numbers for
 *      the indirect blocks(if needed) and the first direct block,
 *      @blks:  on return it will store the total number of allocated
 *              direct blocks
 */
static int ext4_alloc_blocks(handle_t *handle, struct inode *inode,
                                ext4_lblk_t iblock, ext4_fsblk_t goal,
                                int indirect_blks, int blks,
                                ext4_fsblk_t new_blocks[4], int *err)
{
        int target, i;
        unsigned long count = 0, blk_allocated = 0;
        int index = 0;
        ext4_fsblk_t current_block = 0;
        int ret = 0;

        /*
         * Here we try to allocate the requested multiple blocks at once,
         * on a best-effort basis.
         * To build a branch, we should allocate blocks for
         * the indirect blocks(if not allocated yet), and at least
         * the first direct block of this branch.  That's the
         * minimum number of blocks need to allocate(required)
         */
        /* first we try to allocate the indirect blocks */
        target = indirect_blks;
        while (target > 0) {
                count = target;
                /* allocating blocks for indirect blocks and direct blocks */
                current_block = ext4_new_meta_blocks(handle, inode,
                                                        goal, &count, err);
                if (*err)
                        goto failed_out;

                target -= count;
                /* allocate blocks for indirect blocks */
                while (index < indirect_blks && count) {
                        new_blocks[index++] = current_block++;
                        count--;
                }
                if (count > 0) {
                        /*
                         * save the new block number
                         * for the first direct block
                         */
                        new_blocks[index] = current_block;
                        printk(KERN_INFO "%s returned more blocks than "
                                                "requested\n", __func__);
                        WARN_ON(1);
                        break;
                }
        }

        target = blks - count ;
        blk_allocated = count;
        if (!target)
                goto allocated;
        /* Now allocate data blocks */
        count = target;
        /* allocating blocks for data blocks */
        current_block = ext4_new_blocks(handle, inode, iblock,
                                                goal, &count, err);
        if (*err && (target == blks)) {
                /*
                 * if the allocation failed and we didn't allocate
                 * any blocks before
                 */
                goto failed_out;
        }
        if (!*err) {
                if (target == blks) {
                /*
                 * save the new block number
                 * for the first direct block
                 */
                        new_blocks[index] = current_block;
                }
                blk_allocated += count;
        }
allocated:
        /* total number of blocks allocated for direct blocks */
        ret = blk_allocated;
        *err = 0;
        return ret;
failed_out:
        for (i = 0; i <index; i++)
                ext4_free_blocks(handle, inode, new_blocks[i], 1, 0);
        return ret;
}

/**
 *      ext4_alloc_branch - allocate and set up a chain of blocks.
 *      @inode: owner
 *      @indirect_blks: number of allocated indirect blocks
 *      @blks: number of allocated direct blocks
 *      @offsets: offsets (in the blocks) to store the pointers to next.
 *      @branch: place to store the chain in.
 *
 *      This function allocates blocks, zeroes out all but the last one,
 *      links them into chain and (if we are synchronous) writes them to disk.
 *      In other words, it prepares a branch that can be spliced onto the
 *      inode. It stores the information about that chain in the branch[], in
 *      the same format as ext4_get_branch() would do. We are calling it after
 *      we had read the existing part of chain and partial points to the last
 *      triple of that (one with zero ->key). Upon the exit we have the same
 *      picture as after the successful ext4_get_block(), except that in one
 *      place chain is disconnected - *branch->p is still zero (we did not
 *      set the last link), but branch->key contains the number that should
 *      be placed into *branch->p to fill that gap.
 *
 *      If allocation fails we free all blocks we've allocated (and forget
 *      their buffer_heads) and return the error value the from failed
 *      ext4_alloc_block() (normally -ENOSPC). Otherwise we set the chain
 *      as described above and return 0.
 */
static int ext4_alloc_branch(handle_t *handle, struct inode *inode,
                                ext4_lblk_t iblock, int indirect_blks,
                                int *blks, ext4_fsblk_t goal,
                                ext4_lblk_t *offsets, Indirect *branch)
{
        int blocksize = inode->i_sb->s_blocksize;
        int i, n = 0;
        int err = 0;
        struct buffer_head *bh;
        int num;
        ext4_fsblk_t new_blocks[4];
        ext4_fsblk_t current_block;

        num = ext4_alloc_blocks(handle, inode, iblock, goal, indirect_blks,
                                *blks, new_blocks, &err);
        if (err)
                return err;

        branch[0].key = cpu_to_le32(new_blocks[0]);
        /*
         * metadata blocks and data blocks are allocated.
         */
        for (n = 1; n <= indirect_blks;  n++) {
                /*
                 * Get buffer_head for parent block, zero it out
                 * and set the pointer to new one, then send
                 * parent to disk.
                 */
                bh = sb_getblk(inode->i_sb, new_blocks[n-1]);
                branch[n].bh = bh;
                lock_buffer(bh);
                BUFFER_TRACE(bh, "call get_create_access");
                err = ext4_journal_get_create_access(handle, bh);
                if (err) {
                        unlock_buffer(bh);
                        brelse(bh);
                        goto failed;
                }

                memset(bh->b_data, 0, blocksize);
                branch[n].p = (__le32 *) bh->b_data + offsets[n];
                branch[n].key = cpu_to_le32(new_blocks[n]);
                *branch[n].p = branch[n].key;
                if ( n == indirect_blks) {
                        current_block = new_blocks[n];
                        /*
                         * End of chain, update the last new metablock of
                         * the chain to point to the new allocated
                         * data blocks numbers
                         */
                        for (i=1; i < num; i++)
                                *(branch[n].p + i) = cpu_to_le32(++current_block);
                }
                BUFFER_TRACE(bh, "marking uptodate");
                set_buffer_uptodate(bh);
                unlock_buffer(bh);

                BUFFER_TRACE(bh, "call ext4_journal_dirty_metadata");
                err = ext4_journal_dirty_metadata(handle, bh);
                if (err)
                        goto failed;
        }
        *blks = num;
        return err;
failed:
        /* Allocation failed, free what we already allocated */
        for (i = 1; i <= n ; i++) {
                BUFFER_TRACE(branch[i].bh, "call jbd2_journal_forget");
                ext4_journal_forget(handle, branch[i].bh);
        }
        for (i = 0; i <indirect_blks; i++)
                ext4_free_blocks(handle, inode, new_blocks[i], 1, 0);

        ext4_free_blocks(handle, inode, new_blocks[i], num, 0);

        return err;
}

/**
 * ext4_splice_branch - splice the allocated branch onto inode.
 * @inode: owner
 * @block: (logical) number of block we are adding
 * @chain: chain of indirect blocks (with a missing link - see
 *      ext4_alloc_branch)
 * @where: location of missing link
 * @num:   number of indirect blocks we are adding
 * @blks:  number of direct blocks we are adding
 *
 * This function fills the missing link and does all housekeeping needed in
 * inode (->i_blocks, etc.). In case of success we end up with the full
 * chain to new block and return 0.
 */
static int ext4_splice_branch(handle_t *handle, struct inode *inode,
                        ext4_lblk_t block, Indirect *where, int num, int blks)
{
        int i;
        int err = 0;
        struct ext4_block_alloc_info *block_i;
        ext4_fsblk_t current_block;

        block_i = EXT4_I(inode)->i_block_alloc_info;
        /*
         * If we're splicing into a [td]indirect block (as opposed to the
         * inode) then we need to get write access to the [td]indirect block
         * before the splice.
         */
        if (where->bh) {
                BUFFER_TRACE(where->bh, "get_write_access");
                err = ext4_journal_get_write_access(handle, where->bh);
                if (err)
                        goto err_out;
        }
        /* That's it */

        *where->p = where->key;

        /*
         * Update the host buffer_head or inode to point to more just allocated
         * direct blocks blocks
         */
        if (num == 0 && blks > 1) {
                current_block = le32_to_cpu(where->key) + 1;
                for (i = 1; i < blks; i++)
                        *(where->p + i ) = cpu_to_le32(current_block++);
        }

        /*
         * update the most recently allocated logical & physical block
         * in i_block_alloc_info, to assist find the proper goal block for next
         * allocation
         */
        if (block_i) {
                block_i->last_alloc_logical_block = block + blks - 1;
                block_i->last_alloc_physical_block =
                                le32_to_cpu(where[num].key) + blks - 1;
        }

        /* We are done with atomic stuff, now do the rest of housekeeping */

        inode->i_ctime = ext4_current_time(inode);
        ext4_mark_inode_dirty(handle, inode);

        /* had we spliced it onto indirect block? */
        if (where->bh) {
                /*
                 * If we spliced it onto an indirect block, we haven't
                 * altered the inode.  Note however that if it is being spliced
                 * onto an indirect block at the very end of the file (the
                 * file is growing) then we *will* alter the inode to reflect
                 * the new i_size.  But that is not done here - it is done in
                 * generic_commit_write->__mark_inode_dirty->ext4_dirty_inode.
                 */
                jbd_debug(5, "splicing indirect only\n");
                BUFFER_TRACE(where->bh, "call ext4_journal_dirty_metadata");
                err = ext4_journal_dirty_metadata(handle, where->bh);
                if (err)
                        goto err_out;
        } else {
                /*
                 * OK, we spliced it into the inode itself on a direct block.
                 * Inode was dirtied above.
                 */
                jbd_debug(5, "splicing direct\n");
        }
        return err;

err_out:
        for (i = 1; i <= num; i++) {
                BUFFER_TRACE(where[i].bh, "call jbd2_journal_forget");
                ext4_journal_forget(handle, where[i].bh);
                ext4_free_blocks(handle, inode,
                                        le32_to_cpu(where[i-1].key), 1, 0);
        }
        ext4_free_blocks(handle, inode, le32_to_cpu(where[num].key), blks, 0);

        return err;
}

/*
 * Allocation strategy is simple: if we have to allocate something, we will
 * have to go the whole way to leaf. So let's do it before attaching anything
 * to tree, set linkage between the newborn blocks, write them if sync is
 * required, recheck the path, free and repeat if check fails, otherwise
 * set the last missing link (that will protect us from any truncate-generated
 * removals - all blocks on the path are immune now) and possibly force the
 * write on the parent block.
 * That has a nice additional property: no special recovery from the failed
 * allocations is needed - we simply release blocks and do not touch anything
 * reachable from inode.
 *
 * `handle' can be NULL if create == 0.
 *
 * return > 0, # of blocks mapped or allocated.
 * return = 0, if plain lookup failed.
 * return < 0, error case.
 *
 *
 * Need to be called with
 * down_read(&EXT4_I(inode)->i_data_sem) if not allocating file system block
 * (ie, create is zero). Otherwise down_write(&EXT4_I(inode)->i_data_sem)
 */
int ext4_get_blocks_handle(handle_t *handle, struct inode *inode,
                ext4_lblk_t iblock, unsigned long maxblocks,
                struct buffer_head *bh_result,
                int create, int extend_disksize)
{
        int err = -EIO;
        ext4_lblk_t offsets[4];
        Indirect chain[4];
        Indirect *partial;
        ext4_fsblk_t goal;
        int indirect_blks;
        int blocks_to_boundary = 0;
        int depth;
        struct ext4_inode_info *ei = EXT4_I(inode);
        int count = 0;
        ext4_fsblk_t first_block = 0;
        loff_t disksize;


        J_ASSERT(!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL));
        J_ASSERT(handle != NULL || create == 0);
        depth = ext4_block_to_path(inode, iblock, offsets,
                                        &blocks_to_boundary);

        if (depth == 0)
                goto out;

        partial = ext4_get_branch(inode, depth, offsets, chain, &err);

        /* Simplest case - block found, no allocation needed */
        if (!partial) {
                first_block = le32_to_cpu(chain[depth - 1].key);
                clear_buffer_new(bh_result);
                count++;
                /*map more blocks*/
                while (count < maxblocks && count <= blocks_to_boundary) {
                        ext4_fsblk_t blk;

                        blk = le32_to_cpu(*(chain[depth-1].p + count));

                        if (blk == first_block + count)
                                count++;
                        else
                                break;
                }
                goto got_it;
        }

        /* Next simple case - plain lookup or failed read of indirect block */
        if (!create || err == -EIO)
                goto cleanup;

        /*
         * Okay, we need to do block allocation.  Lazily initialize the block
         * allocation info here if necessary
        */
        if (S_ISREG(inode->i_mode) && (!ei->i_block_alloc_info))
                ext4_init_block_alloc_info(inode);

        goal = ext4_find_goal(inode, iblock, partial);

        /* the number of blocks need to allocate for [d,t]indirect blocks */
        indirect_blks = (chain + depth) - partial - 1;

        /*
         * Next look up the indirect map to count the totoal number of
         * direct blocks to allocate for this branch.
         */
        count = ext4_blks_to_allocate(partial, indirect_blks,
                                        maxblocks, blocks_to_boundary);
        /*
         * Block out ext4_truncate while we alter the tree
         */
        err = ext4_alloc_branch(handle, inode, iblock, indirect_blks,
                                        &count, goal,
                                        offsets + (partial - chain), partial);

        /*
         * The ext4_splice_branch call will free and forget any buffers
         * on the new chain if there is a failure, but that risks using
         * up transaction credits, especially for bitmaps where the
         * credits cannot be returned.  Can we handle this somehow?  We
         * may need to return -EAGAIN upwards in the worst case.  --sct
         */
        if (!err)
                err = ext4_splice_branch(handle, inode, iblock,
                                        partial, indirect_blks, count);
        /*
         * i_disksize growing is protected by i_data_sem.  Don't forget to
         * protect it if you're about to implement concurrent
         * ext4_get_block() -bzzz
        */
        if (!err && extend_disksize) {
                disksize = ((loff_t) iblock + count) << inode->i_blkbits;
                if (disksize > i_size_read(inode))
                        disksize = i_size_read(inode);
                if (disksize > ei->i_disksize)
                        ei->i_disksize = disksize;
        }
        if (err)
                goto cleanup;

        set_buffer_new(bh_result);
got_it:
        map_bh(bh_result, inode->i_sb, le32_to_cpu(chain[depth-1].key));
        if (count > blocks_to_boundary)
                set_buffer_boundary(bh_result);
        err = count;
        /* Clean up and exit */
        partial = chain + depth - 1;    /* the whole chain */
cleanup:
        while (partial > chain) {
                BUFFER_TRACE(partial->bh, "call brelse");
                brelse(partial->bh);
                partial--;
        }
        BUFFER_TRACE(bh_result, "returned");
out:
        return err;
}

/*
 * Calculate the number of metadata blocks need to reserve
 * to allocate @blocks for non extent file based file
 */
static int ext4_indirect_calc_metadata_amount(struct inode *inode, int blocks)
{
        int icap = EXT4_ADDR_PER_BLOCK(inode->i_sb);
        int ind_blks, dind_blks, tind_blks;

        /* number of new indirect blocks needed */
        ind_blks = (blocks + icap - 1) / icap;

        dind_blks = (ind_blks + icap - 1) / icap;

        tind_blks = 1;

        return ind_blks + dind_blks + tind_blks;
}

/*
 * Calculate the number of metadata blocks need to reserve
 * to allocate given number of blocks
 */
static int ext4_calc_metadata_amount(struct inode *inode, int blocks)
{
        if (!blocks)
                return 0;

        if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL)
                return ext4_ext_calc_metadata_amount(inode, blocks);

        return ext4_indirect_calc_metadata_amount(inode, blocks);
}

static void ext4_da_update_reserve_space(struct inode *inode, int used)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        int total, mdb, mdb_free;

        spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
        /* recalculate the number of metablocks still need to be reserved */
        total = EXT4_I(inode)->i_reserved_data_blocks - used;
        mdb = ext4_calc_metadata_amount(inode, total);

        /* figure out how many metablocks to release */
        BUG_ON(mdb > EXT4_I(inode)->i_reserved_meta_blocks);
        mdb_free = EXT4_I(inode)->i_reserved_meta_blocks - mdb;

        /* Account for allocated meta_blocks */
        mdb_free -= EXT4_I(inode)->i_allocated_meta_blocks;

        /* update fs free blocks counter for truncate case */
        percpu_counter_add(&sbi->s_freeblocks_counter, mdb_free);

        /* update per-inode reservations */
        BUG_ON(used  > EXT4_I(inode)->i_reserved_data_blocks);
        EXT4_I(inode)->i_reserved_data_blocks -= used;

        BUG_ON(mdb > EXT4_I(inode)->i_reserved_meta_blocks);
        EXT4_I(inode)->i_reserved_meta_blocks = mdb;
        EXT4_I(inode)->i_allocated_meta_blocks = 0;
        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
}

/*
 * The ext4_get_blocks_wrap() function try to look up the requested blocks,
 * and returns if the blocks are already mapped.
 *
 * Otherwise it takes the write lock of the i_data_sem and allocate blocks
 * and store the allocated blocks in the result buffer head and mark it
 * mapped.
 *
 * If file type is extents based, it will call ext4_ext_get_blocks(),
 * Otherwise, call with ext4_get_blocks_handle() to handle indirect mapping
 * based files
 *
 * On success, it returns the number of blocks being mapped or allocate.
 * if create==0 and the blocks are pre-allocated and uninitialized block,
 * the result buffer head is unmapped. If the create ==1, it will make sure
 * the buffer head is mapped.
 *
 * It returns 0 if plain look up failed (blocks have not been allocated), in
 * that casem, buffer head is unmapped
 *
 * It returns the error in case of allocation failure.
 */
int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
                        unsigned long max_blocks, struct buffer_head *bh,
                        int create, int extend_disksize, int flag)
{
        int retval;

        clear_buffer_mapped(bh);

        /*
         * Try to see if we can get  the block without requesting
         * for new file system block.
         */
        down_read((&EXT4_I(inode)->i_data_sem));
        if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
                retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
                                bh, 0, 0);
        } else {
                retval = ext4_get_blocks_handle(handle,
                                inode, block, max_blocks, bh, 0, 0);
        }
        up_read((&EXT4_I(inode)->i_data_sem));

        /* If it is only a block(s) look up */
        if (!create)
                return retval;

        /*
         * Returns if the blocks have already allocated
         *
         * Note that if blocks have been preallocated
         * ext4_ext_get_block() returns th create = 0
         * with buffer head unmapped.
         */
        if (retval > 0 && buffer_mapped(bh))
                return retval;

        /*
         * New blocks allocate and/or writing to uninitialized extent
         * will possibly result in updating i_data, so we take
         * the write lock of i_data_sem, and call get_blocks()
         * with create == 1 flag.
         */
        down_write((&EXT4_I(inode)->i_data_sem));

        /*
         * if the caller is from delayed allocation writeout path
         * we have already reserved fs blocks for allocation
         * let the underlying get_block() function know to
         * avoid double accounting
         */
        if (flag)
                EXT4_I(inode)->i_delalloc_reserved_flag = 1;
        /*
         * We need to check for EXT4 here because migrate
         * could have changed the inode type in between
         */
        if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
                retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
                                bh, create, extend_disksize);
        } else {
                retval = ext4_get_blocks_handle(handle, inode, block,
                                max_blocks, bh, create, extend_disksize);

                if (retval > 0 && buffer_new(bh)) {
                        /*
                         * We allocated new blocks which will result in
                         * i_data's format changing.  Force the migrate
                         * to fail by clearing migrate flags
                         */
                        EXT4_I(inode)->i_flags = EXT4_I(inode)->i_flags &
                                                        ~EXT4_EXT_MIGRATE;
                }
        }

        if (flag) {
                EXT4_I(inode)->i_delalloc_reserved_flag = 0;
                /*
                 * Update reserved blocks/metadata blocks
                 * after successful block allocation
                 * which were deferred till now
                 */
                if ((retval > 0) && buffer_delay(bh))
                        ext4_da_update_reserve_space(inode, retval);
        }

        up_write((&EXT4_I(inode)->i_data_sem));
        return retval;
}

/* Maximum number of blocks we map for direct IO at once. */
#define DIO_MAX_BLOCKS 4096

static int ext4_get_block(struct inode *inode, sector_t iblock,
                        struct buffer_head *bh_result, int create)
{
        handle_t *handle = ext4_journal_current_handle();
        int ret = 0, started = 0;
        unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
        int dio_credits;

        if (create && !handle) {
                /* Direct IO write... */
                if (max_blocks > DIO_MAX_BLOCKS)
                        max_blocks = DIO_MAX_BLOCKS;
                dio_credits = ext4_chunk_trans_blocks(inode, max_blocks);
                handle = ext4_journal_start(inode, dio_credits);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        goto out;
                }
                started = 1;
        }

        ret = ext4_get_blocks_wrap(handle, inode, iblock,
                                        max_blocks, bh_result, create, 0, 0);
        if (ret > 0) {
                bh_result->b_size = (ret << inode->i_blkbits);
                ret = 0;
        }
        if (started)
                ext4_journal_stop(handle);
out:
        return ret;
}

/*
 * `handle' can be NULL if create is zero
 */
struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
                                ext4_lblk_t block, int create, int *errp)
{
        struct buffer_head dummy;
        int fatal = 0, err;

        J_ASSERT(handle != NULL || create == 0);

        dummy.b_state = 0;
        dummy.b_blocknr = -1000;
        buffer_trace_init(&dummy.b_history);
        err = ext4_get_blocks_wrap(handle, inode, block, 1,
                                        &dummy, create, 1, 0);
        /*
         * ext4_get_blocks_handle() returns number of blocks
         * mapped. 0 in case of a HOLE.
         */
        if (err > 0) {
                if (err > 1)
                        WARN_ON(1);
                err = 0;
        }
        *errp = err;
        if (!err && buffer_mapped(&dummy)) {
                struct buffer_head *bh;
                bh = sb_getblk(inode->i_sb, dummy.b_blocknr);
                if (!bh) {
                        *errp = -EIO;
                        goto err;
                }
                if (buffer_new(&dummy)) {
                        J_ASSERT(create != 0);
                        J_ASSERT(handle != NULL);

                        /*
                         * Now that we do not always journal data, we should
                         * keep in mind whether this should always journal the
                         * new buffer as metadata.  For now, regular file
                         * writes use ext4_get_block instead, so it's not a
                         * problem.
                         */
                        lock_buffer(bh);
                        BUFFER_TRACE(bh, "call get_create_access");
                        fatal = ext4_journal_get_create_access(handle, bh);
                        if (!fatal && !buffer_uptodate(bh)) {
                                memset(bh->b_data,0,inode->i_sb->s_blocksize);
                                set_buffer_uptodate(bh);
                        }
                        unlock_buffer(bh);
                        BUFFER_TRACE(bh, "call ext4_journal_dirty_metadata");
                        err = ext4_journal_dirty_metadata(handle, bh);
                        if (!fatal)
                                fatal = err;
                } else {
                        BUFFER_TRACE(bh, "not a new buffer");
                }
                if (fatal) {
                        *errp = fatal;
                        brelse(bh);
                        bh = NULL;
                }
                return bh;
        }
err:
        return NULL;
}

struct buffer_head *ext4_bread(handle_t *handle, struct inode *inode,
                               ext4_lblk_t block, int create, int *err)
{
        struct buffer_head * bh;

        bh = ext4_getblk(handle, inode, block, create, err);
        if (!bh)
                return bh;
        if (buffer_uptodate(bh))
                return bh;
        ll_rw_block(READ_META, 1, &bh);
        wait_on_buffer(bh);
        if (buffer_uptodate(bh))
                return bh;
        put_bh(bh);
        *err = -EIO;
        return NULL;
}

static int walk_page_buffers(   handle_t *handle,
                                struct buffer_head *head,
                                unsigned from,
                                unsigned to,
                                int *partial,
                                int (*fn)(      handle_t *handle,
                                                struct buffer_head *bh))
{
        struct buffer_head *bh;
        unsigned block_start, block_end;
        unsigned blocksize = head->b_size;
        int err, ret = 0;
        struct buffer_head *next;

        for (   bh = head, block_start = 0;
                ret == 0 && (bh != head || !block_start);
                block_start = block_end, bh = next)
        {
                next = bh->b_this_page;
                block_end = block_start + blocksize;
                if (block_end <= from || block_start >= to) {
                        if (partial && !buffer_uptodate(bh))
                                *partial = 1;
                        continue;
                }
                err = (*fn)(handle, bh);
                if (!ret)
                        ret = err;
        }
        return ret;
}

/*
 * To preserve ordering, it is essential that the hole instantiation and
 * the data write be encapsulated in a single transaction.  We cannot
 * close off a transaction and start a new one between the ext4_get_block()
 * and the commit_write().  So doing the jbd2_journal_start at the start of
 * prepare_write() is the right place.
 *
 * Also, this function can nest inside ext4_writepage() ->
 * block_write_full_page(). In that case, we *know* that ext4_writepage()
 * has generated enough buffer credits to do the whole page.  So we won't
 * block on the journal in that case, which is good, because the caller may
 * be PF_MEMALLOC.
 *
 * By accident, ext4 can be reentered when a transaction is open via
 * quota file writes.  If we were to commit the transaction while thus
 * reentered, there can be a deadlock - we would be holding a quota
 * lock, and the commit would never complete if another thread had a
 * transaction open and was blocking on the quota lock - a ranking
 * violation.
 *
 * So what we do is to rely on the fact that jbd2_journal_stop/journal_start
 * will _not_ run commit under these circumstances because handle->h_ref
 * is elevated.  We'll still have enough credits for the tiny quotafile
 * write.
 */
static int do_journal_get_write_access(handle_t *handle,
                                        struct buffer_head *bh)
{
        if (!buffer_mapped(bh) || buffer_freed(bh))
                return 0;
        return ext4_journal_get_write_access(handle, bh);
}

static int ext4_write_begin(struct file *file, struct address_space *mapping,
                                loff_t pos, unsigned len, unsigned flags,
                                struct page **pagep, void **fsdata)
{
        struct inode *inode = mapping->host;
        int ret, needed_blocks = ext4_writepage_trans_blocks(inode);
        handle_t *handle;
        int retries = 0;
        struct page *page;
        pgoff_t index;
        unsigned from, to;

        index = pos >> PAGE_CACHE_SHIFT;
        from = pos & (PAGE_CACHE_SIZE - 1);
        to = from + len;

retry:
        handle = ext4_journal_start(inode, needed_blocks);
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                goto out;
        }

        page = __grab_cache_page(mapping, index);
        if (!page) {
                ext4_journal_stop(handle);
                ret = -ENOMEM;
                goto out;
        }
        *pagep = page;

        ret = block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
                                                        ext4_get_block);

        if (!ret && ext4_should_journal_data(inode)) {
                ret = walk_page_buffers(handle, page_buffers(page),
                                from, to, NULL, do_journal_get_write_access);
        }

        if (ret) {
                unlock_page(page);
                ext4_journal_stop(handle);
                page_cache_release(page);
        }

        if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
                goto retry;
out:
        return ret;
}

/* For write_end() in data=journal mode */
static int write_end_fn(handle_t *handle, struct buffer_head *bh)
{
        if (!buffer_mapped(bh) || buffer_freed(bh))
                return 0;
        set_buffer_uptodate(bh);
        return ext4_journal_dirty_metadata(handle, bh);
}

/*
 * We need to pick up the new inode size which generic_commit_write gave us
 * `file' can be NULL - eg, when called from page_symlink().
 *
 * ext4 never places buffers on inode->i_mapping->private_list.  metadata
 * buffers are managed internally.
 */
static int ext4_ordered_write_end(struct file *file,
                                struct address_space *mapping,
                                loff_t pos, unsigned len, unsigned copied,
                                struct page *page, void *fsdata)
{
        handle_t *handle = ext4_journal_current_handle();
        struct inode *inode = mapping->host;
        int ret = 0, ret2;

        ret = ext4_jbd2_file_inode(handle, inode);

        if (ret == 0) {
                /*
                 * generic_write_end() will run mark_inode_dirty() if i_size
                 * changes.  So let's piggyback the i_disksize mark_inode_dirty
                 * into that.
                 */
                loff_t new_i_size;

                new_i_size = pos + copied;
                if (new_i_size > EXT4_I(inode)->i_disksize)
                        EXT4_I(inode)->i_disksize = new_i_size;
                ret2 = generic_write_end(file, mapping, pos, len, copied,
                                                        page, fsdata);
                copied = ret2;
                if (ret2 < 0)
                        ret = ret2;
        }
        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;

        return ret ? ret : copied;
}

static int ext4_writeback_write_end(struct file *file,
                                struct address_space *mapping,
                                loff_t pos, unsigned len, unsigned copied,
                                struct page *page, void *fsdata)
{
        handle_t *handle = ext4_journal_current_handle();
        struct inode *inode = mapping->host;
        int ret = 0, ret2;
        loff_t new_i_size;

        new_i_size = pos + copied;
        if (new_i_size > EXT4_I(inode)->i_disksize)
                EXT4_I(inode)->i_disksize = new_i_size;

        ret2 = generic_write_end(file, mapping, pos, len, copied,
                                                        page, fsdata);
        copied = ret2;
        if (ret2 < 0)
                ret = ret2;

        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;

        return ret ? ret : copied;
}

static int ext4_journalled_write_end(struct file *file,
                                struct address_space *mapping,
                                loff_t pos, unsigned len, unsigned copied,
                                struct page *page, void *fsdata)
{
        handle_t *handle = ext4_journal_current_handle();
        struct inode *inode = mapping->host;
        int ret = 0, ret2;
        int partial = 0;
        unsigned from, to;

        from = pos & (PAGE_CACHE_SIZE - 1);
        to = from + len;

        if (copied < len) {
                if (!PageUptodate(page))
                        copied = 0;
                page_zero_new_buffers(page, from+copied, to);
        }

        ret = walk_page_buffers(handle, page_buffers(page), from,
                                to, &partial, write_end_fn);
        if (!partial)
                SetPageUptodate(page);
        if (pos+copied > inode->i_size)
                i_size_write(inode, pos+copied);
        EXT4_I(inode)->i_state |= EXT4_STATE_JDATA;
        if (inode->i_size > EXT4_I(inode)->i_disksize) {
                EXT4_I(inode)->i_disksize = inode->i_size;
                ret2 = ext4_mark_inode_dirty(handle, inode);
                if (!ret)
                        ret = ret2;
        }

        unlock_page(page);
        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;
        page_cache_release(page);

        return ret ? ret : copied;
}

static int ext4_da_reserve_space(struct inode *inode, int nrblocks)
{
       struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
       unsigned long md_needed, mdblocks, total = 0;

        /*
         * recalculate the amount of metadata blocks to reserve
         * in order to allocate nrblocks
         * worse case is one extent per block
         */
        spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
        total = EXT4_I(inode)->i_reserved_data_blocks + nrblocks;
        mdblocks = ext4_calc_metadata_amount(inode, total);
        BUG_ON(mdblocks < EXT4_I(inode)->i_reserved_meta_blocks);

        md_needed = mdblocks - EXT4_I(inode)->i_reserved_meta_blocks;
        total = md_needed + nrblocks;

        if (ext4_has_free_blocks(sbi, total) < total) {
                spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
                return -ENOSPC;
        }
        /* reduce fs free blocks counter */
        percpu_counter_sub(&sbi->s_freeblocks_counter, total);

        EXT4_I(inode)->i_reserved_data_blocks += nrblocks;
        EXT4_I(inode)->i_reserved_meta_blocks = mdblocks;

        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
        return 0;       /* success */
}

static void ext4_da_release_space(struct inode *inode, int to_free)
{
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        int total, mdb, mdb_free, release;

        if (!to_free)
                return;         /* Nothing to release, exit */

        spin_lock(&EXT4_I(inode)->i_block_reservation_lock);

        if (!EXT4_I(inode)->i_reserved_data_blocks) {
                /*
                 * if there is no reserved blocks, but we try to free some
                 * then the counter is messed up somewhere.
                 * but since this function is called from invalidate
                 * page, it's harmless to return without any action
                 */
                printk(KERN_INFO "ext4 delalloc try to release %d reserved "
                            "blocks for inode %lu, but there is no reserved "
                            "data blocks\n", to_free, inode->i_ino);
                spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
                return;
        }

        /* recalculate the number of metablocks still need to be reserved */
        total = EXT4_I(inode)->i_reserved_data_blocks - to_free;
        mdb = ext4_calc_metadata_amount(inode, total);

        /* figure out how many metablocks to release */
        BUG_ON(mdb > EXT4_I(inode)->i_reserved_meta_blocks);
        mdb_free = EXT4_I(inode)->i_reserved_meta_blocks - mdb;

        release = to_free + mdb_free;

        /* update fs free blocks counter for truncate case */
        percpu_counter_add(&sbi->s_freeblocks_counter, release);

        /* update per-inode reservations */
        BUG_ON(to_free > EXT4_I(inode)->i_reserved_data_blocks);
        EXT4_I(inode)->i_reserved_data_blocks -= to_free;

        BUG_ON(mdb > EXT4_I(inode)->i_reserved_meta_blocks);
        EXT4_I(inode)->i_reserved_meta_blocks = mdb;
        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
}

static void ext4_da_page_release_reservation(struct page *page,
                                                unsigned long offset)
{
        int to_release = 0;
        struct buffer_head *head, *bh;
        unsigned int curr_off = 0;

        head = page_buffers(page);
        bh = head;
        do {
                unsigned int next_off = curr_off + bh->b_size;

                if ((offset <= curr_off) && (buffer_delay(bh))) {
                        to_release++;
                        clear_buffer_delay(bh);
                }
                curr_off = next_off;
        } while ((bh = bh->b_this_page) != head);
        ext4_da_release_space(page->mapping->host, to_release);
}

/*
 * Delayed allocation stuff
 */

struct mpage_da_data {
        struct inode *inode;
        struct buffer_head lbh;                 /* extent of blocks */
        unsigned long first_page, next_page;    /* extent of pages */
        get_block_t *get_block;
        struct writeback_control *wbc;
        int io_done;
        long pages_written;
};

/*
 * mpage_da_submit_io - walks through extent of pages and try to write
 * them with writepage() call back
 *
 * @mpd->inode: inode
 * @mpd->first_page: first page of the extent
 * @mpd->next_page: page after the last page of the extent
 * @mpd->get_block: the filesystem's block mapper function
 *
 * By the time mpage_da_submit_io() is called we expect all blocks
 * to be allocated. this may be wrong if allocation failed.
 *
 * As pages are already locked by write_cache_pages(), we can't use it
 */
static int mpage_da_submit_io(struct mpage_da_data *mpd)
{
        struct address_space *mapping = mpd->inode->i_mapping;
        int ret = 0, err, nr_pages, i;
        unsigned long index, end;
        struct pagevec pvec;

        BUG_ON(mpd->next_page <= mpd->first_page);
        pagevec_init(&pvec, 0);
        index = mpd->first_page;
        end = mpd->next_page - 1;

        while (index <= end) {
                /* XXX: optimize tail */
                nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
                if (nr_pages == 0)
                        break;
                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];

                        index = page->index;
                        if (index > end)
                                break;
                        index++;

                        err = mapping->a_ops->writepage(page, mpd->wbc);
                        if (!err)
                                mpd->pages_written++;
                        /*
                         * In error case, we have to continue because
                         * remaining pages are still locked
                         * XXX: unlock and re-dirty them?
                         */
                        if (ret == 0)
                                ret = err;
                }
                pagevec_release(&pvec);
        }
        return ret;
}

/*
 * mpage_put_bnr_to_bhs - walk blocks and assign them actual numbers
 *
 * @mpd->inode - inode to walk through
 * @exbh->b_blocknr - first block on a disk
 * @exbh->b_size - amount of space in bytes
 * @logical - first logical block to start assignment with
 *
 * the function goes through all passed space and put actual disk
 * block numbers into buffer heads, dropping BH_Delay
 */
static void mpage_put_bnr_to_bhs(struct mpage_da_data *mpd, sector_t logical,
                                 struct buffer_head *exbh)
{
        struct inode *inode = mpd->inode;
        struct address_space *mapping = inode->i_mapping;
        int blocks = exbh->b_size >> inode->i_blkbits;
        sector_t pblock = exbh->b_blocknr, cur_logical;
        struct buffer_head *head, *bh;
        pgoff_t index, end;
        struct pagevec pvec;
        int nr_pages, i;

        index = logical >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
        end = (logical + blocks - 1) >> (PAGE_CACHE_SHIFT - inode->i_blkbits);
        cur_logical = index << (PAGE_CACHE_SHIFT - inode->i_blkbits);

        pagevec_init(&pvec, 0);

        while (index <= end) {
                /* XXX: optimize tail */
                nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
                if (nr_pages == 0)
                        break;
                for (i = 0; i < nr_pages; i++) {
                        struct page *page = pvec.pages[i];

                        index = page->index;
                        if (index > end)
                                break;
                        index++;

                        BUG_ON(!PageLocked(page));
                        BUG_ON(PageWriteback(page));
                        BUG_ON(!page_has_buffers(page));

                        bh = page_buffers(page);
                        head = bh;

                        /* skip blocks out of the range */
                        do {
                                if (cur_logical >= logical)
                                        break;
                                cur_logical++;
                        } while ((bh = bh->b_this_page) != head);

                        do {
                                if (cur_logical >= logical + blocks)
                                        break;
                                if (buffer_delay(bh)) {
                                        bh->b_blocknr = pblock;
                                        clear_buffer_delay(bh);
                                        bh->b_bdev = inode->i_sb->s_bdev;
                                } else if (buffer_unwritten(bh)) {
                                        bh->b_blocknr = pblock;
                                        clear_buffer_unwritten(bh);
                                        set_buffer_mapped(bh);
                                        set_buffer_new(bh);
                                        bh->b_bdev = inode->i_sb->s_bdev;
                                } else if (buffer_mapped(bh))
                                        BUG_ON(bh->b_blocknr != pblock);

                                cur_logical++;
                                pblock++;
                        } while ((bh = bh->b_this_page) != head);
                }
                pagevec_release(&pvec);
        }
}


/*
 * __unmap_underlying_blocks - just a helper function to unmap
 * set of blocks described by @bh
 */
static inline void __unmap_underlying_blocks(struct inode *inode,
                                             struct buffer_head *bh)
{
        struct block_device *bdev = inode->i_sb->s_bdev;
        int blocks, i;

        blocks = bh->b_size >> inode->i_blkbits;
        for (i = 0; i < blocks; i++)
                unmap_underlying_metadata(bdev, bh->b_blocknr + i);
}

/*
 * mpage_da_map_blocks - go through given space
 *
 * @mpd->lbh - bh describing space
 * @mpd->get_block - the filesystem's block mapper function
 *
 * The function skips space we know is already mapped to disk blocks.
 *
 */
static void mpage_da_map_blocks(struct mpage_da_data *mpd)
{
        int err = 0;
        struct buffer_head *lbh = &mpd->lbh;
        sector_t next = lbh->b_blocknr;
        struct buffer_head new;

        /*
         * We consider only non-mapped and non-allocated blocks
         */
        if (buffer_mapped(lbh) && !buffer_delay(lbh))
                return;

        new.b_state = lbh->b_state;
        new.b_blocknr = 0;
        new.b_size = lbh->b_size;

        /*
         * If we didn't accumulate anything
         * to write simply return
         */
        if (!new.b_size)
                return;
        err = mpd->get_block(mpd->inode, next, &new, 1);
        if (err)
                return;
        BUG_ON(new.b_size == 0);

        if (buffer_new(&new))
                __unmap_underlying_blocks(mpd->inode, &new);

        /*
         * If blocks are delayed marked, we need to
         * put actual blocknr and drop delayed bit
         */
        if (buffer_delay(lbh) || buffer_unwritten(lbh))
                mpage_put_bnr_to_bhs(mpd, next, &new);

        return;
}

#define BH_FLAGS ((1 << BH_Uptodate) | (1 << BH_Mapped) | \
                (1 << BH_Delay) | (1 << BH_Unwritten))

/*
 * mpage_add_bh_to_extent - try to add one more block to extent of blocks
 *
 * @mpd->lbh - extent of blocks
 * @logical - logical number of the block in the file
 * @bh - bh of the block (used to access block's state)
 *
 * the function is used to collect contig. blocks in same state
 */
static void mpage_add_bh_to_extent(struct mpage_da_data *mpd,
                                   sector_t logical, struct buffer_head *bh)
{
        sector_t next;
        size_t b_size = bh->b_size;
        struct buffer_head *lbh = &mpd->lbh;
        int nrblocks = lbh->b_size >> mpd->inode->i_blkbits;

        /* check if thereserved journal credits might overflow */
        if (!(EXT4_I(mpd->inode)->i_flags & EXT4_EXTENTS_FL)) {
                if (nrblocks >= EXT4_MAX_TRANS_DATA) {
                        /*
                         * With non-extent format we are limited by the journal
                         * credit available.  Total credit needed to insert
                         * nrblocks contiguous blocks is dependent on the
                         * nrblocks.  So limit nrblocks.
                         */
                        goto flush_it;
                } else if ((nrblocks + (b_size >> mpd->inode->i_blkbits)) >
                                EXT4_MAX_TRANS_DATA) {
                        /*
                         * Adding the new buffer_head would make it cross the
                         * allowed limit for which we have journal credit
                         * reserved. So limit the new bh->b_size
                         */
                        b_size = (EXT4_MAX_TRANS_DATA - nrblocks) <<
                                                mpd->inode->i_blkbits;
                        /* we will do mpage_da_submit_io in the next loop */
                }
        }
        /*
         * First block in the extent
         */
        if (lbh->b_size == 0) {
                lbh->b_blocknr = logical;
                lbh->b_size = b_size;
                lbh->b_state = bh->b_state & BH_FLAGS;
                return;
        }

        next = lbh->b_blocknr + nrblocks;
        /*
         * Can we merge the block to our big extent?
         */
        if (logical == next && (bh->b_state & BH_FLAGS) == lbh->b_state) {
                lbh->b_size += b_size;
                return;
        }

flush_it:
        /*
         * We couldn't merge the block to our extent, so we
         * need to flush current  extent and start new one
         */
        mpage_da_map_blocks(mpd);
        mpage_da_submit_io(mpd);
        mpd->io_done = 1;
        return;
}

/*
 * __mpage_da_writepage - finds extent of pages and blocks
 *
 * @page: page to consider
 * @wbc: not used, we just follow rules
 * @data: context
 *
 * The function finds extents of pages and scan them for all blocks.
 */
static int __mpage_da_writepage(struct page *page,
                                struct writeback_control *wbc, void *data)
{
        struct mpage_da_data *mpd = data;
        struct inode *inode = mpd->inode;
        struct buffer_head *bh, *head, fake;
        sector_t logical;

        if (mpd->io_done) {
                /*
                 * Rest of the page in the page_vec
                 * redirty then and skip then. We will
                 * try to to write them again after
                 * starting a new transaction
                 */
                redirty_page_for_writepage(wbc, page);
                unlock_page(page);
                return MPAGE_DA_EXTENT_TAIL;
        }
        /*
         * Can we merge this page to current extent?
         */
        if (mpd->next_page != page->index) {
                /*
                 * Nope, we can't. So, we map non-allocated blocks
                 * and start IO on them using writepage()
                 */
                if (mpd->next_page != mpd->first_page) {
                        mpage_da_map_blocks(mpd);
                        mpage_da_submit_io(mpd);
                        /*
                         * skip rest of the page in the page_vec
                         */
                        mpd->io_done = 1;
                        redirty_page_for_writepage(wbc, page);
                        unlock_page(page);
                        return MPAGE_DA_EXTENT_TAIL;
                }

                /*
                 * Start next extent of pages ...
                 */
                mpd->first_page = page->index;

                /*
                 * ... and blocks
                 */
                mpd->lbh.b_size = 0;
                mpd->lbh.b_state = 0;
                mpd->lbh.b_blocknr = 0;
        }

        mpd->next_page = page->index + 1;
        logical = (sector_t) page->index <<
                  (PAGE_CACHE_SHIFT - inode->i_blkbits);

        if (!page_has_buffers(page)) {
                /*
                 * There is no attached buffer heads yet (mmap?)
                 * we treat the page asfull of dirty blocks
                 */
                bh = &fake;
                bh->b_size = PAGE_CACHE_SIZE;
                bh->b_state = 0;
                set_buffer_dirty(bh);
                set_buffer_uptodate(bh);
                mpage_add_bh_to_extent(mpd, logical, bh);
                if (mpd->io_done)
                        return MPAGE_DA_EXTENT_TAIL;
        } else {
                /*
                 * Page with regular buffer heads, just add all dirty ones
                 */
                head = page_buffers(page);
                bh = head;
                do {
                        BUG_ON(buffer_locked(bh));
                        if (buffer_dirty(bh) &&
                                (!buffer_mapped(bh) || buffer_delay(bh))) {
                                mpage_add_bh_to_extent(mpd, logical, bh);
                                if (mpd->io_done)
                                        return MPAGE_DA_EXTENT_TAIL;
                        }
                        logical++;
                } while ((bh = bh->b_this_page) != head);
        }

        return 0;
}

/*
 * mpage_da_writepages - walk the list of dirty pages of the given
 * address space, allocates non-allocated blocks, maps newly-allocated
 * blocks to existing bhs and issue IO them
 *
 * @mapping: address space structure to write
 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 * @get_block: the filesystem's block mapper function.
 *
 * This is a library function, which implements the writepages()
 * address_space_operation.
 */
static int mpage_da_writepages(struct address_space *mapping,
                               struct writeback_control *wbc,
                               get_block_t get_block)
{
        struct mpage_da_data mpd;
        long to_write;
        int ret;

        if (!get_block)
                return generic_writepages(mapping, wbc);

        mpd.wbc = wbc;
        mpd.inode = mapping->host;
        mpd.lbh.b_size = 0;
        mpd.lbh.b_state = 0;
        mpd.lbh.b_blocknr = 0;
        mpd.first_page = 0;
        mpd.next_page = 0;
        mpd.get_block = get_block;
        mpd.io_done = 0;
        mpd.pages_written = 0;

        to_write = wbc->nr_to_write;

        ret = write_cache_pages(mapping, wbc, __mpage_da_writepage, &mpd);

        /*
         * Handle last extent of pages
         */
        if (!mpd.io_done && mpd.next_page != mpd.first_page) {
                mpage_da_map_blocks(&mpd);
                mpage_da_submit_io(&mpd);
        }

        wbc->nr_to_write = to_write - mpd.pages_written;
        return ret;
}

/*
 * this is a special callback for ->write_begin() only
 * it's intention is to return mapped block or reserve space
 */
static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
                                  struct buffer_head *bh_result, int create)
{
        int ret = 0;

        BUG_ON(create == 0);
        BUG_ON(bh_result->b_size != inode->i_sb->s_blocksize);

        /*
         * first, we need to know whether the block is allocated already
         * preallocated blocks are unmapped but should treated
         * the same as allocated blocks.
         */
        ret = ext4_get_blocks_wrap(NULL, inode, iblock, 1,  bh_result, 0, 0, 0);
        if ((ret == 0) && !buffer_delay(bh_result)) {
                /* the block isn't (pre)allocated yet, let's reserve space */
                /*
                 * XXX: __block_prepare_write() unmaps passed block,
                 * is it OK?
                 */
                ret = ext4_da_reserve_space(inode, 1);
                if (ret)
                        /* not enough space to reserve */
                        return ret;

                map_bh(bh_result, inode->i_sb, 0);
                set_buffer_new(bh_result);
                set_buffer_delay(bh_result);
        } else if (ret > 0) {
                bh_result->b_size = (ret << inode->i_blkbits);
                ret = 0;
        }

        return ret;
}
#define         EXT4_DELALLOC_RSVED     1
static int ext4_da_get_block_write(struct inode *inode, sector_t iblock,
                                   struct buffer_head *bh_result, int create)
{
        int ret;
        unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
        loff_t disksize = EXT4_I(inode)->i_disksize;
        handle_t *handle = NULL;

        handle = ext4_journal_current_handle();
        if (!handle) {
                ret = ext4_get_blocks_wrap(handle, inode, iblock, max_blocks,
                                   bh_result, 0, 0, 0);
                BUG_ON(!ret);
        } else {
                ret = ext4_get_blocks_wrap(handle, inode, iblock, max_blocks,
                                   bh_result, create, 0, EXT4_DELALLOC_RSVED);
        }

        if (ret > 0) {
                bh_result->b_size = (ret << inode->i_blkbits);

                /*
                 * Update on-disk size along with block allocation
                 * we don't use 'extend_disksize' as size may change
                 * within already allocated block -bzzz
                 */
                disksize = ((loff_t) iblock + ret) << inode->i_blkbits;
                if (disksize > i_size_read(inode))
                        disksize = i_size_read(inode);
                if (disksize > EXT4_I(inode)->i_disksize) {
                        /*
                         * XXX: replace with spinlock if seen contended -bzzz
                         */
                        down_write(&EXT4_I(inode)->i_data_sem);
                        if (disksize > EXT4_I(inode)->i_disksize)
                                EXT4_I(inode)->i_disksize = disksize;
                        up_write(&EXT4_I(inode)->i_data_sem);

                        if (EXT4_I(inode)->i_disksize == disksize) {
                                ret = ext4_mark_inode_dirty(handle, inode);
                                return ret;
                        }
                }
                ret = 0;
        }
        return ret;
}

static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
{
        /*
         * unmapped buffer is possible for holes.
         * delay buffer is possible with delayed allocation
         */
        return ((!buffer_mapped(bh) || buffer_delay(bh)) && buffer_dirty(bh));
}

static int ext4_normal_get_block_write(struct inode *inode, sector_t iblock,
                                   struct buffer_head *bh_result, int create)
{
        int ret = 0;
        unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;

        /*
         * we don't want to do block allocation in writepage
         * so call get_block_wrap with create = 0
         */
        ret = ext4_get_blocks_wrap(NULL, inode, iblock, max_blocks,
                                   bh_result, 0, 0, 0);
        if (ret > 0) {
                bh_result->b_size = (ret << inode->i_blkbits);
                ret = 0;
        }
        return ret;
}

/*
 * get called vi ext4_da_writepages after taking page lock (have journal handle)
 * get called via journal_submit_inode_data_buffers (no journal handle)
 * get called via shrink_page_list via pdflush (no journal handle)
 * or grab_page_cache when doing write_begin (have journal handle)
 */
static int ext4_da_writepage(struct page *page,
                                struct writeback_control *wbc)
{
        int ret = 0;
        loff_t size;
        unsigned long len;
        struct buffer_head *page_bufs;
        struct inode *inode = page->mapping->host;

        size = i_size_read(inode);
        if (page->index == size >> PAGE_CACHE_SHIFT)
                len = size & ~PAGE_CACHE_MASK;
        else
                len = PAGE_CACHE_SIZE;

        if (page_has_buffers(page)) {
                page_bufs = page_buffers(page);
                if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
                                        ext4_bh_unmapped_or_delay)) {
                        /*
                         * We don't want to do  block allocation
                         * So redirty the page and return
                         * We may reach here when we do a journal commit
                         * via journal_submit_inode_data_buffers.
                         * If we don't have mapping block we just ignore
                         * them. We can also reach here via shrink_page_list
                         */
                        redirty_page_for_writepage(wbc, page);
                        unlock_page(page);
                        return 0;
                }
        } else {
                /*
                 * The test for page_has_buffers() is subtle:
                 * We know the page is dirty but it lost buffers. That means
                 * that at some moment in time after write_begin()/write_end()
                 * has been called all buffers have been clean and thus they
                 * must have been written at least once. So they are all
                 * mapped and we can happily proceed with mapping them
                 * and writing the page.
                 *
                 * Try to initialize the buffer_heads and check whether
                 * all are mapped and non delay. We don't want to
                 * do block allocation here.
                 */
                ret = block_prepare_write(page, 0, PAGE_CACHE_SIZE,
                                                ext4_normal_get_block_write);
                if (!ret) {
                        page_bufs = page_buffers(page);
                        /* check whether all are mapped and non delay */
                        if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
                                                ext4_bh_unmapped_or_delay)) {
                                redirty_page_for_writepage(wbc, page);
                                unlock_page(page);
                                return 0;
                        }
                } else {
                        /*
                         * We can't do block allocation here
                         * so just redity the page and unlock
                         * and return
                         */
                        redirty_page_for_writepage(wbc, page);
                        unlock_page(page);
                        return 0;
                }
        }

        if (test_opt(inode->i_sb, NOBH) && ext4_should_writeback_data(inode))
                ret = nobh_writepage(page, ext4_normal_get_block_write, wbc);
        else
                ret = block_write_full_page(page,
                                                ext4_normal_get_block_write,
                                                wbc);

        return ret;
}

/*
 * This is called via ext4_da_writepages() to
 * calulate the total number of credits to reserve to fit
 * a single extent allocation into a single transaction,
 * ext4_da_writpeages() will loop calling this before
 * the block allocation.
 */

static int ext4_da_writepages_trans_blocks(struct inode *inode)
{
        int max_blocks = EXT4_I(inode)->i_reserved_data_blocks;

        /*
         * With non-extent format the journal credit needed to
         * insert nrblocks contiguous block is dependent on
         * number of contiguous block. So we will limit
         * number of contiguous block to a sane value
         */
        if (!(inode->i_flags & EXT4_EXTENTS_FL) &&
            (max_blocks > EXT4_MAX_TRANS_DATA))
                max_blocks = EXT4_MAX_TRANS_DATA;

        return ext4_chunk_trans_blocks(inode, max_blocks);
}

static int ext4_da_writepages(struct address_space *mapping,
                              struct writeback_control *wbc)
{
        struct inode *inode = mapping->host;
        handle_t *handle = NULL;
        int needed_blocks;
        int ret = 0;
        long to_write;
        loff_t range_start = 0;
        long pages_skipped = 0;

        /*
         * No pages to write? This is mainly a kludge to avoid starting
         * a transaction for special inodes like journal inode on last iput()
         * because that could violate lock ordering on umount
         */
        if (!mapping->nrpages || !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
                return 0;

        if (!wbc->range_cyclic)
                /*
                 * If range_cyclic is not set force range_cont
                 * and save the old writeback_index
                 */
                wbc->range_cont = 1;

        range_start =  wbc->range_start;
        pages_skipped = wbc->pages_skipped;

restart_loop:
        to_write = wbc->nr_to_write;
        while (!ret && to_write > 0) {

                /*
                 * we  insert one extent at a time. So we need
                 * credit needed for single extent allocation.
                 * journalled mode is currently not supported
                 * by delalloc
                 */
                BUG_ON(ext4_should_journal_data(inode));
                needed_blocks = ext4_da_writepages_trans_blocks(inode);

                /* start a new transaction*/
                handle = ext4_journal_start(inode, needed_blocks);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        printk(KERN_EMERG "%s: jbd2_start: "
                               "%ld pages, ino %lu; err %d\n", __func__,
                                wbc->nr_to_write, inode->i_ino, ret);
                        dump_stack();
                        goto out_writepages;
                }
                if (ext4_should_order_data(inode)) {
                        /*
                         * With ordered mode we need to add
                         * the inode to the journal handl
                         * when we do block allocation.
                         */
                        ret = ext4_jbd2_file_inode(handle, inode);
                        if (ret) {
                                ext4_journal_stop(handle);
                                goto out_writepages;
                        }
                }

                to_write -= wbc->nr_to_write;
                ret = mpage_da_writepages(mapping, wbc,
                                          ext4_da_get_block_write);
                ext4_journal_stop(handle);
                if (ret == MPAGE_DA_EXTENT_TAIL) {
                        /*
                         * got one extent now try with
                         * rest of the pages
                         */
                        to_write += wbc->nr_to_write;
                        ret = 0;
                } else if (wbc->nr_to_write) {
                        /*
                         * There is no more writeout needed
                         * or we requested for a noblocking writeout
                         * and we found the device congested
                         */
                        to_write += wbc->nr_to_write;
                        break;
                }
                wbc->nr_to_write = to_write;
        }

        if (wbc->range_cont && (pages_skipped != wbc->pages_skipped)) {
                /* We skipped pages in this loop */
                wbc->range_start = range_start;
                wbc->nr_to_write = to_write +
                                wbc->pages_skipped - pages_skipped;
                wbc->pages_skipped = pages_skipped;
                goto restart_loop;
        }

out_writepages:
        wbc->nr_to_write = to_write;
        wbc->range_start = range_start;
        return ret;
}

static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
                                loff_t pos, unsigned len, unsigned flags,
                                struct page **pagep, void **fsdata)
{
        int ret, retries = 0;
        struct page *page;
        pgoff_t index;
        unsigned from, to;
        struct inode *inode = mapping->host;
        handle_t *handle;

        index = pos >> PAGE_CACHE_SHIFT;
        from = pos & (PAGE_CACHE_SIZE - 1);
        to = from + len;

retry:
        /*
         * With delayed allocation, we don't log the i_disksize update
         * if there is delayed block allocation. But we still need
         * to journalling the i_disksize update if writes to the end
         * of file which has an already mapped buffer.
         */
        handle = ext4_journal_start(inode, 1);
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                goto out;
        }

        page = __grab_cache_page(mapping, index);
        if (!page) {
                ext4_journal_stop(handle);
                ret = -ENOMEM;
                goto out;
        }
        *pagep = page;

        ret = block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
                                                        ext4_da_get_block_prep);
        if (ret < 0) {
                unlock_page(page);
                ext4_journal_stop(handle);
                page_cache_release(page);
        }

        if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
                goto retry;
out:
        return ret;
}

/*
 * Check if we should update i_disksize
 * when write to the end of file but not require block allocation
 */
static int ext4_da_should_update_i_disksize(struct page *page,
                                         unsigned long offset)
{
        struct buffer_head *bh;
        struct inode *inode = page->mapping->host;
        unsigned int idx;
        int i;

        bh = page_buffers(page);
        idx = offset >> inode->i_blkbits;

        for (i=0; i < idx; i++)
                bh = bh->b_this_page;

        if (!buffer_mapped(bh) || (buffer_delay(bh)))
                return 0;
        return 1;
}

static int ext4_da_write_end(struct file *file,
                                struct address_space *mapping,
                                loff_t pos, unsigned len, unsigned copied,
                                struct page *page, void *fsdata)
{
        struct inode *inode = mapping->host;
        int ret = 0, ret2;
        handle_t *handle = ext4_journal_current_handle();
        loff_t new_i_size;
        unsigned long start, end;

        start = pos & (PAGE_CACHE_SIZE - 1);
        end = start + copied -1;

        /*
         * generic_write_end() will run mark_inode_dirty() if i_size
         * changes.  So let's piggyback the i_disksize mark_inode_dirty
         * into that.
         */

        new_i_size = pos + copied;
        if (new_i_size > EXT4_I(inode)->i_disksize) {
                if (ext4_da_should_update_i_disksize(page, end)) {
                        down_write(&EXT4_I(inode)->i_data_sem);
                        if (new_i_size > EXT4_I(inode)->i_disksize) {
                                /*
                                 * Updating i_disksize when extending file
                                 * without needing block allocation
                                 */
                                if (ext4_should_order_data(inode))
                                        ret = ext4_jbd2_file_inode(handle,
                                                                   inode);

                                EXT4_I(inode)->i_disksize = new_i_size;
                        }
                        up_write(&EXT4_I(inode)->i_data_sem);
                }
        }
        ret2 = generic_write_end(file, mapping, pos, len, copied,
                                                        page, fsdata);
        copied = ret2;
        if (ret2 < 0)
                ret = ret2;
        ret2 = ext4_journal_stop(handle);
        if (!ret)
                ret = ret2;

        return ret ? ret : copied;
}

static void ext4_da_invalidatepage(struct page *page, unsigned long offset)
{
        /*
         * Drop reserved blocks
         */
        BUG_ON(!PageLocked(page));
        if (!page_has_buffers(page))
                goto out;

        ext4_da_page_release_reservation(page, offset);

out:
        ext4_invalidatepage(page, offset);

        return;
}


/*
 * bmap() is special.  It gets used by applications such as lilo and by
 * the swapper to find the on-disk block of a specific piece of data.
 *
 * Naturally, this is dangerous if the block concerned is still in the
 * journal.  If somebody makes a swapfile on an ext4 data-journaling
 * filesystem and enables swap, then they may get a nasty shock when the
 * data getting swapped to that swapfile suddenly gets overwritten by
 * the original zero's written out previously to the journal and
 * awaiting writeback in the kernel's buffer cache.
 *
 * So, if we see any bmap calls here on a modified, data-journaled file,
 * take extra steps to flush any blocks which might be in the cache.
 */
static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
{
        struct inode *inode = mapping->host;
        journal_t *journal;
        int err;

        if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
                        test_opt(inode->i_sb, DELALLOC)) {
                /*
                 * With delalloc we want to sync the file
                 * so that we can make sure we allocate
                 * blocks for file
                 */
                filemap_write_and_wait(mapping);
        }

        if (EXT4_I(inode)->i_state & EXT4_STATE_JDATA) {
                /*
                 * This is a REALLY heavyweight approach, but the use of
                 * bmap on dirty files is expected to be extremely rare:
                 * only if we run lilo or swapon on a freshly made file
                 * do we expect this to happen.
                 *
                 * (bmap requires CAP_SYS_RAWIO so this does not
                 * represent an unprivileged user DOS attack --- we'd be
                 * in trouble if mortal users could trigger this path at
                 * will.)
                 *
                 * NB. EXT4_STATE_JDATA is not set on files other than
                 * regular files.  If somebody wants to bmap a directory
                 * or symlink and gets confused because the buffer
                 * hasn't yet been flushed to disk, they deserve
                 * everything they get.
                 */

                EXT4_I(inode)->i_state &= ~EXT4_STATE_JDATA;
                journal = EXT4_JOURNAL(inode);
                jbd2_journal_lock_updates(journal);
                err = jbd2_journal_flush(journal);
                jbd2_journal_unlock_updates(journal);

                if (err)
                        return 0;
        }

        return generic_block_bmap(mapping,block,ext4_get_block);
}

static int bget_one(handle_t *handle, struct buffer_head *bh)
{
        get_bh(bh);
        return 0;
}

static int bput_one(handle_t *handle, struct buffer_head *bh)
{
        put_bh(bh);
        return 0;
}

/*
 * Note that we don't need to start a transaction unless we're journaling data
 * because we should have holes filled from ext4_page_mkwrite(). We even don't
 * need to file the inode to the transaction's list in ordered mode because if
 * we are writing back data added by write(), the inode is already there and if
 * we are writing back data modified via mmap(), noone guarantees in which
 * transaction the data will hit the disk. In case we are journaling data, we
 * cannot start transaction directly because transaction start ranks above page
 * lock so we have to do some magic.
 *
 * In all journaling modes block_write_full_page() will start the I/O.
 *
 * Problem:
 *
 *      ext4_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
 *              ext4_writepage()
 *
 * Similar for:
 *
 *      ext4_file_write() -> generic_file_write() -> __alloc_pages() -> ...
 *
 * Same applies to ext4_get_block().  We will deadlock on various things like
 * lock_journal and i_data_sem
 *
 * Setting PF_MEMALLOC here doesn't work - too many internal memory
 * allocations fail.
 *
 * 16May01: If we're reentered then journal_current_handle() will be
 *          non-zero. We simply *return*.
 *
 * 1 July 2001: @@@ FIXME:
 *   In journalled data mode, a data buffer may be metadata against the
 *   current transaction.  But the same file is part of a shared mapping
 *   and someone does a writepage() on it.
 *
 *   We will move the buffer onto the async_data list, but *after* it has
 *   been dirtied. So there's a small window where we have dirty data on
 *   BJ_Metadata.
 *
 *   Note that this only applies to the last partial page in the file.  The
 *   bit which block_write_full_page() uses prepare/commit for.  (That's
 *   broken code anyway: it's wrong for msync()).
 *
 *   It's a rare case: affects the final partial page, for journalled data
 *   where the file is subject to bith write() and writepage() in the same
 *   transction.  To fix it we'll need a custom block_write_full_page().
 *   We'll probably need that anyway for journalling writepage() output.
 *
 * We don't honour synchronous mounts for writepage().  That would be
 * disastrous.  Any write() or metadata operation will sync the fs for
 * us.
 *
 */
static int __ext4_normal_writepage(struct page *page,
                                struct writeback_control *wbc)
{
        struct inode *inode = page->mapping->host;

        if (test_opt(inode->i_sb, NOBH))
                return nobh_writepage(page,
                                        ext4_normal_get_block_write, wbc);
        else
                return block_write_full_page(page,
                                                ext4_normal_get_block_write,
                                                wbc);
}

static int ext4_normal_writepage(struct page *page,
                                struct writeback_control *wbc)
{
        struct inode *inode = page->mapping->host;
        loff_t size = i_size_read(inode);
        loff_t len;

        J_ASSERT(PageLocked(page));
        if (page->index == size >> PAGE_CACHE_SHIFT)
                len = size & ~PAGE_CACHE_MASK;
        else
                len = PAGE_CACHE_SIZE;

        if (page_has_buffers(page)) {
                /* if page has buffers it should all be mapped
                 * and allocated. If there are not buffers attached
                 * to the page we know the page is dirty but it lost
                 * buffers. That means that at some moment in time
                 * after write_begin() / write_end() has been called
                 * all buffers have been clean and thus they must have been
                 * written at least once. So they are all mapped and we can
                 * happily proceed with mapping them and writing the page.
                 */
                BUG_ON(walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
                                        ext4_bh_unmapped_or_delay));
        }

        if (!ext4_journal_current_handle())
                return __ext4_normal_writepage(page, wbc);

        redirty_page_for_writepage(wbc, page);
        unlock_page(page);
        return 0;
}

static int __ext4_journalled_writepage(struct page *page,
                                struct writeback_control *wbc)
{
        struct address_space *mapping = page->mapping;
        struct inode *inode = mapping->host;
        struct buffer_head *page_bufs;
        handle_t *handle = NULL;
        int ret = 0;
        int err;

        ret = block_prepare_write(page, 0, PAGE_CACHE_SIZE,
                                        ext4_normal_get_block_write);
        if (ret != 0)
                goto out_unlock;

        page_bufs = page_buffers(page);
        walk_page_buffers(handle, page_bufs, 0, PAGE_CACHE_SIZE, NULL,
                                                                bget_one);
        /* As soon as we unlock the page, it can go away, but we have
         * references to buffers so we are safe */
        unlock_page(page);

        handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
        if (IS_ERR(handle)) {
                ret = PTR_ERR(handle);
                goto out;
        }

        ret = walk_page_buffers(handle, page_bufs, 0,
                        PAGE_CACHE_SIZE, NULL, do_journal_get_write_access);

        err = walk_page_buffers(handle, page_bufs, 0,
                                PAGE_CACHE_SIZE, NULL, write_end_fn);
        if (ret == 0)
                ret = err;
        err = ext4_journal_stop(handle);
        if (!ret)
                ret = err;

        walk_page_buffers(handle, page_bufs, 0,
                                PAGE_CACHE_SIZE, NULL, bput_one);
        EXT4_I(inode)->i_state |= EXT4_STATE_JDATA;
        goto out;

out_unlock:
        unlock_page(page);
out:
        return ret;
}

static int ext4_journalled_writepage(struct page *page,
                                struct writeback_control *wbc)
{
        struct inode *inode = page->mapping->host;
        loff_t size = i_size_read(inode);
        loff_t len;

        J_ASSERT(PageLocked(page));
        if (page->index == size >> PAGE_CACHE_SHIFT)
                len = size & ~PAGE_CACHE_MASK;
        else
                len = PAGE_CACHE_SIZE;

        if (page_has_buffers(page)) {
                /* if page has buffers it should all be mapped
                 * and allocated. If there are not buffers attached
                 * to the page we know the page is dirty but it lost
                 * buffers. That means that at some moment in time
                 * after write_begin() / write_end() has been called
                 * all buffers have been clean and thus they must have been
                 * written at least once. So they are all mapped and we can
                 * happily proceed with mapping them and writing the page.
                 */
                BUG_ON(walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
                                        ext4_bh_unmapped_or_delay));
        }

        if (ext4_journal_current_handle())
                goto no_write;

        if (PageChecked(page)) {
                /*
                 * It's mmapped pagecache.  Add buffers and journal it.  There
                 * doesn't seem much point in redirtying the page here.
                 */
                ClearPageChecked(page);
                return __ext4_journalled_writepage(page, wbc);
        } else {
                /*
                 * It may be a page full of checkpoint-mode buffers.  We don't
                 * really know unless we go poke around in the buffer_heads.
                 * But block_write_full_page will do the right thing.
                 */
                return block_write_full_page(page,
                                                ext4_normal_get_block_write,
                                                wbc);
        }
no_write:
        redirty_page_for_writepage(wbc, page);
        unlock_page(page);
        return 0;
}

static int ext4_readpage(struct file *file, struct page *page)
{
        return mpage_readpage(page, ext4_get_block);
}

static int
ext4_readpages(struct file *file, struct address_space *mapping,
                struct list_head *pages, unsigned nr_pages)
{
        return mpage_readpages(mapping, pages, nr_pages, ext4_get_block);
}

static void ext4_invalidatepage(struct page *page, unsigned long offset)
{
        journal_t *journal = EXT4_JOURNAL(page->mapping->host);

        /*
         * If it's a full truncate we just forget about the pending dirtying
         */
        if (offset == 0)
                ClearPageChecked(page);

        jbd2_journal_invalidatepage(journal, page, offset);
}

static int ext4_releasepage(struct page *page, gfp_t wait)
{
        journal_t *journal = EXT4_JOURNAL(page->mapping->host);

        WARN_ON(PageChecked(page));
        if (!page_has_buffers(page))
                return 0;
        return jbd2_journal_try_to_free_buffers(journal, page, wait);
}

/*
 * If the O_DIRECT write will extend the file then add this inode to the
 * orphan list.  So recovery will truncate it back to the original size
 * if the machine crashes during the write.
 *
 * If the O_DIRECT write is intantiating holes inside i_size and the machine
 * crashes then stale disk data _may_ be exposed inside the file. But current
 * VFS code falls back into buffered path in that case so we are safe.
 */
static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb,
                        const struct iovec *iov, loff_t offset,
                        unsigned long nr_segs)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file->f_mapping->host;
        struct ext4_inode_info *ei = EXT4_I(inode);
        handle_t *handle;
        ssize_t ret;
        int orphan = 0;
        size_t count = iov_length(iov, nr_segs);

        if (rw == WRITE) {
                loff_t final_size = offset + count;

                if (final_size > inode->i_size) {
                        /* Credits for sb + inode write */
                        handle = ext4_journal_start(inode, 2);
                        if (IS_ERR(handle)) {
                                ret = PTR_ERR(handle);
                                goto out;
                        }
                        ret = ext4_orphan_add(handle, inode);
                        if (ret) {
                                ext4_journal_stop(handle);
                                goto out;
                        }
                        orphan = 1;
                        ei->i_disksize = inode->i_size;
                        ext4_journal_stop(handle);
                }
        }

        ret = blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov,
                                 offset, nr_segs,
                                 ext4_get_block, NULL);

        if (orphan) {
                int err;

                /* Credits for sb + inode write */
                handle = ext4_journal_start(inode, 2);
                if (IS_ERR(handle)) {
                        /* This is really bad luck. We've written the data
                         * but cannot extend i_size. Bail out and pretend
                         * the write failed... */
                        ret = PTR_ERR(handle);
                        goto out;
                }
                if (inode->i_nlink)
                        ext4_orphan_del(handle, inode);
                if (ret > 0) {
                        loff_t end = offset + ret;
                        if (end > inode->i_size) {
                                ei->i_disksize = end;
                                i_size_write(inode, end);
                                /*
                                 * We're going to return a positive `ret'
                                 * here due to non-zero-length I/O, so there's
                                 * no way of reporting error returns from
                                 * ext4_mark_inode_dirty() to userspace.  So
                                 * ignore it.
                                 */
                                ext4_mark_inode_dirty(handle, inode);
                        }
                }
                err = ext4_journal_stop(handle);
                if (ret == 0)
                        ret = err;
        }
out:
        return ret;
}

/*
 * Pages can be marked dirty completely asynchronously from ext4's journalling
 * activity.  By filemap_sync_pte(), try_to_unmap_one(), etc.  We cannot do
 * much here because ->set_page_dirty is called under VFS locks.  The page is
 * not necessarily locked.
 *
 * We cannot just dirty the page and leave attached buffers clean, because the
 * buffers' dirty state is "definitive".  We cannot just set the buffers dirty
 * or jbddirty because all the journalling code will explode.
 *
 * So what we do is to mark the page "pending dirty" and next time writepage
 * is called, propagate that into the buffers appropriately.
 */
static int ext4_journalled_set_page_dirty(struct page *page)
{
        SetPageChecked(page);
        return __set_page_dirty_nobuffers(page);
}

static const struct address_space_operations ext4_ordered_aops = {
        .readpage               = ext4_readpage,
        .readpages              = ext4_readpages,
        .writepage              = ext4_normal_writepage,
        .sync_page              = block_sync_page,
        .write_begin            = ext4_write_begin,
        .write_end              = ext4_ordered_write_end,
        .bmap                   = ext4_bmap,
        .invalidatepage         = ext4_invalidatepage,
        .releasepage            = ext4_releasepage,
        .direct_IO              = ext4_direct_IO,
        .migratepage            = buffer_migrate_page,
        .is_partially_uptodate  = block_is_partially_uptodate,
};

static const struct address_space_operations ext4_writeback_aops = {
        .readpage               = ext4_readpage,
        .readpages              = ext4_readpages,
        .writepage              = ext4_normal_writepage,
        .sync_page              = block_sync_page,
        .write_begin            = ext4_write_begin,
        .write_end              = ext4_writeback_write_end,
        .bmap                   = ext4_bmap,
        .invalidatepage         = ext4_invalidatepage,
        .releasepage            = ext4_releasepage,
        .direct_IO              = ext4_direct_IO,
        .migratepage            = buffer_migrate_page,
        .is_partially_uptodate  = block_is_partially_uptodate,
};

static const struct address_space_operations ext4_journalled_aops = {
        .readpage               = ext4_readpage,
        .readpages              = ext4_readpages,
        .writepage              = ext4_journalled_writepage,
        .sync_page              = block_sync_page,
        .write_begin            = ext4_write_begin,
        .write_end              = ext4_journalled_write_end,
        .set_page_dirty         = ext4_journalled_set_page_dirty,
        .bmap                   = ext4_bmap,
        .invalidatepage         = ext4_invalidatepage,
        .releasepage            = ext4_releasepage,
        .is_partially_uptodate  = block_is_partially_uptodate,
};

static const struct address_space_operations ext4_da_aops = {
        .readpage               = ext4_readpage,
        .readpages              = ext4_readpages,
        .writepage              = ext4_da_writepage,
        .writepages             = ext4_da_writepages,
        .sync_page              = block_sync_page,
        .write_begin            = ext4_da_write_begin,
        .write_end              = ext4_da_write_end,
        .bmap                   = ext4_bmap,
        .invalidatepage         = ext4_da_invalidatepage,
        .releasepage            = ext4_releasepage,
        .direct_IO              = ext4_direct_IO,
        .migratepage            = buffer_migrate_page,
        .is_partially_uptodate  = block_is_partially_uptodate,
};

void ext4_set_aops(struct inode *inode)
{
        if (ext4_should_order_data(inode) &&
                test_opt(inode->i_sb, DELALLOC))
                inode->i_mapping->a_ops = &ext4_da_aops;
        else if (ext4_should_order_data(inode))
                inode->i_mapping->a_ops = &ext4_ordered_aops;
        else if (ext4_should_writeback_data(inode) &&
                 test_opt(inode->i_sb, DELALLOC))
                inode->i_mapping->a_ops = &ext4_da_aops;
        else if (ext4_should_writeback_data(inode))
                inode->i_mapping->a_ops = &ext4_writeback_aops;
        else
                inode->i_mapping->a_ops = &ext4_journalled_aops;
}

/*
 * ext4_block_truncate_page() zeroes out a mapping from file offset `from'
 * up to the end of the block which corresponds to `from'.
 * This required during truncate. We need to physically zero the tail end
 * of that block so it doesn't yield old data if the file is later grown.
 */
int ext4_block_truncate_page(handle_t *handle,
                struct address_space *mapping, loff_t from)
{
        ext4_fsblk_t index = from >> PAGE_CACHE_SHIFT;
        unsigned offset = from & (PAGE_CACHE_SIZE-1);
        unsigned blocksize, length, pos;
        ext4_lblk_t iblock;
        struct inode *inode = mapping->host;
        struct buffer_head *bh;
        struct page *page;
        int err = 0;

        page = grab_cache_page(mapping, from >> PAGE_CACHE_SHIFT);
        if (!page)
                return -EINVAL;

        blocksize = inode->i_sb->s_blocksize;
        length = blocksize - (offset & (blocksize - 1));
        iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);

        /*
         * For "nobh" option,  we can only work if we don't need to
         * read-in the page - otherwise we create buffers to do the IO.
         */
        if (!page_has_buffers(page) && test_opt(inode->i_sb, NOBH) &&
             ext4_should_writeback_data(inode) && PageUptodate(page)) {
                zero_user(page, offset, length);
                set_page_dirty(page);
                goto unlock;
        }

        if (!page_has_buffers(page))
                create_empty_buffers(page, blocksize, 0);

        /* Find the buffer that contains "offset" */
        bh = page_buffers(page);
        pos = blocksize;
        while (offset >= pos) {
                bh = bh->b_this_page;
                iblock++;
                pos += blocksize;
        }

        err = 0;
        if (buffer_freed(bh)) {
                BUFFER_TRACE(bh, "freed: skip");
                goto unlock;
        }

        if (!buffer_mapped(bh)) {
                BUFFER_TRACE(bh, "unmapped");
                ext4_get_block(inode, iblock, bh, 0);
                /* unmapped? It's a hole - nothing to do */
                if (!buffer_mapped(bh)) {
                        BUFFER_TRACE(bh, "still unmapped");
                        goto unlock;
                }
        }

        /* Ok, it's mapped. Make sure it's up-to-date */
        if (PageUptodate(page))
                set_buffer_uptodate(bh);

        if (!buffer_uptodate(bh)) {
                err = -EIO;
                ll_rw_block(READ, 1, &bh);
                wait_on_buffer(bh);
                /* Uhhuh. Read error. Complain and punt. */
                if (!buffer_uptodate(bh))
                        goto unlock;
        }

        if (ext4_should_journal_data(inode)) {
                BUFFER_TRACE(bh, "get write access");
                err = ext4_journal_get_write_access(handle, bh);
                if (err)
                        goto unlock;
        }

        zero_user(page, offset, length);

        BUFFER_TRACE(bh, "zeroed end of block");

        err = 0;
        if (ext4_should_journal_data(inode)) {
                err = ext4_journal_dirty_metadata(handle, bh);
        } else {
                if (ext4_should_order_data(inode))
                        err = ext4_jbd2_file_inode(handle, inode);
                mark_buffer_dirty(bh);
        }

unlock:
        unlock_page(page);
        page_cache_release(page);
        return err;
}

/*
 * Probably it should be a library function... search for first non-zero word
 * or memcmp with zero_page, whatever is better for particular architecture.
 * Linus?
 */
static inline int all_zeroes(__le32 *p, __le32 *q)
{
        while (p < q)
                if (*p++)
                        return 0;
        return 1;
}

/**
 *      ext4_find_shared - find the indirect blocks for partial truncation.
 *      @inode:   inode in question
 *      @depth:   depth of the affected branch
 *      @offsets: offsets of pointers in that branch (see ext4_block_to_path)
 *      @chain:   place to store the pointers to partial indirect blocks
 *      @top:     place to the (detached) top of branch
 *
 *      This is a helper function used by ext4_truncate().
 *
 *      When we do truncate() we may have to clean the ends of several
 *      indirect blocks but leave the blocks themselves alive. Block is
 *      partially truncated if some data below the new i_size is refered
 *      from it (and it is on the path to the first completely truncated
 *      data block, indeed).  We have to free the top of that path along
 *      with everything to the right of the path. Since no allocation
 *      past the truncation point is possible until ext4_truncate()
 *      finishes, we may safely do the latter, but top of branch may
 *      require special attention - pageout below the truncation point
 *      might try to populate it.
 *
 *      We atomically detach the top of branch from the tree, store the
 *      block number of its root in *@top, pointers to buffer_heads of
 *      partially truncated blocks - in @chain[].bh and pointers to
 *      their last elements that should not be removed - in
 *      @chain[].p. Return value is the pointer to last filled element
 *      of @chain.
 *
 *      The work left to caller to do the actual freeing of subtrees:
 *              a) free the subtree starting from *@top
 *              b) free the subtrees whose roots are stored in
 *                      (@chain[i].p+1 .. end of @chain[i].bh->b_data)
 *              c) free the subtrees growing from the inode past the @chain[0].
 *                      (no partially truncated stuff there).  */

static Indirect *ext4_find_shared(struct inode *inode, int depth,
                        ext4_lblk_t offsets[4], Indirect chain[4], __le32 *top)
{
        Indirect *partial, *p;
        int k, err;

        *top = 0;
        /* Make k index the deepest non-null offest + 1 */
        for (k = depth; k > 1 && !offsets[k-1]; k--)
                ;
        partial = ext4_get_branch(inode, k, offsets, chain, &err);
        /* Writer: pointers */
        if (!partial)
                partial = chain + k-1;
        /*
         * If the branch acquired continuation since we've looked at it -
         * fine, it should all survive and (new) top doesn't belong to us.
         */
        if (!partial->key && *partial->p)
                /* Writer: end */
                goto no_top;
        for (p=partial; p>chain && all_zeroes((__le32*)p->bh->b_data,p->p); p--)
                ;
        /*
         * OK, we've found the last block that must survive. The rest of our
         * branch should be detached before unlocking. However, if that rest
         * of branch is all ours and does not grow immediately from the inode
         * it's easier to cheat and just decrement partial->p.
         */
        if (p == chain + k - 1 && p > chain) {
                p->p--;
        } else {
                *top = *p->p;
                /* Nope, don't do this in ext4.  Must leave the tree intact */
#if 0
                *p->p = 0;
#endif
        }
        /* Writer: end */

        while(partial > p) {
                brelse(partial->bh);
                partial--;
        }
no_top:
        return partial;
}

/*
 * Zero a number of block pointers in either an inode or an indirect block.
 * If we restart the transaction we must again get write access to the
 * indirect block for further modification.
 *
 * We release `count' blocks on disk, but (last - first) may be greater
 * than `count' because there can be holes in there.
 */
static void ext4_clear_blocks(handle_t *handle, struct inode *inode,
                struct buffer_head *bh, ext4_fsblk_t block_to_free,
                unsigned long count, __le32 *first, __le32 *last)
{
        __le32 *p;
        if (try_to_extend_transaction(handle, inode)) {
                if (bh) {
                        BUFFER_TRACE(bh, "call ext4_journal_dirty_metadata");
                        ext4_journal_dirty_metadata(handle, bh);
                }
                ext4_mark_inode_dirty(handle, inode);
                ext4_journal_test_restart(handle, inode);
                if (bh) {
                        BUFFER_TRACE(bh, "retaking write access");
                        ext4_journal_get_write_access(handle, bh);
                }
        }

        /*
         * Any buffers which are on the journal will be in memory. We find
         * them on the hash table so jbd2_journal_revoke() will run jbd2_journal_forget()
         * on them.  We've already detached each block from the file, so
         * bforget() in jbd2_journal_forget() should be safe.
         *
         * AKPM: turn on bforget in jbd2_journal_forget()!!!
         */
        for (p = first; p < last; p++) {
                u32 nr = le32_to_cpu(*p);
                if (nr) {
                        struct buffer_head *tbh;

                        *p = 0;
                        tbh = sb_find_get_block(inode->i_sb, nr);
                        ext4_forget(handle, 0, inode, tbh, nr);
                }
        }

        ext4_free_blocks(handle, inode, block_to_free, count, 0);
}

/**
 * ext4_free_data - free a list of data blocks
 * @handle:     handle for this transaction
 * @inode:      inode we are dealing with
 * @this_bh:    indirect buffer_head which contains *@first and *@last
 * @first:      array of block numbers
 * @last:       points immediately past the end of array
 *
 * We are freeing all blocks refered from that array (numbers are stored as
 * little-endian 32-bit) and updating @inode->i_blocks appropriately.
 *
 * We accumulate contiguous runs of blocks to free.  Conveniently, if these
 * blocks are contiguous then releasing them at one time will only affect one
 * or two bitmap blocks (+ group descriptor(s) and superblock) and we won't
 * actually use a lot of journal space.
 *
 * @this_bh will be %NULL if @first and @last point into the inode's direct
 * block pointers.
 */
static void ext4_free_data(handle_t *handle, struct inode *inode,
                           struct buffer_head *this_bh,
                           __le32 *first, __le32 *last)
{
        ext4_fsblk_t block_to_free = 0;    /* Starting block # of a run */
        unsigned long count = 0;            /* Number of blocks in the run */
        __le32 *block_to_free_p = NULL;     /* Pointer into inode/ind
                                               corresponding to
                                               block_to_free */
        ext4_fsblk_t nr;                    /* Current block # */
        __le32 *p;                          /* Pointer into inode/ind
                                               for current block */
        int err;

        if (this_bh) {                          /* For indirect block */
                BUFFER_TRACE(this_bh, "get_write_access");
                err = ext4_journal_get_write_access(handle, this_bh);
                /* Important: if we can't update the indirect pointers
                 * to the blocks, we can't free them. */
                if (err)
                        return;
        }

        for (p = first; p < last; p++) {
                nr = le32_to_cpu(*p);
                if (nr) {
                        /* accumulate blocks to free if they're contiguous */
                        if (count == 0) {
                                block_to_free = nr;
                                block_to_free_p = p;
                                count = 1;
                        } else if (nr == block_to_free + count) {
                                count++;
                        } else {
                                ext4_clear_blocks(handle, inode, this_bh,
                                                  block_to_free,
                                                  count, block_to_free_p, p);
                                block_to_free = nr;
                                block_to_free_p = p;
                                count = 1;
                        }
                }
        }

        if (count > 0)
                ext4_clear_blocks(handle, inode, this_bh, block_to_free,
                                  count, block_to_free_p, p);

        if (this_bh) {
                BUFFER_TRACE(this_bh, "call ext4_journal_dirty_metadata");

                /*
                 * The buffer head should have an attached journal head at this
                 * point. However, if the data is corrupted and an indirect
                 * block pointed to itself, it would have been detached when
                 * the block was cleared. Check for this instead of OOPSing.
                 */
                if (bh2jh(this_bh))
                        ext4_journal_dirty_metadata(handle, this_bh);
                else
                        ext4_error(inode->i_sb, __func__,
                                   "circular indirect block detected, "
                                   "inode=%lu, block=%llu",
                                   inode->i_ino,
                                   (unsigned long long) this_bh->b_blocknr);
        }
}

/**
 *      ext4_free_branches - free an array of branches
 *      @handle: JBD handle for this transaction
 *      @inode: inode we are dealing with
 *      @parent_bh: the buffer_head which contains *@first and *@last
 *      @first: array of block numbers
 *      @last:  pointer immediately past the end of array
 *      @depth: depth of the branches to free
 *
 *      We are freeing all blocks refered from these branches (numbers are
 *      stored as little-endian 32-bit) and updating @inode->i_blocks
 *      appropriately.
 */
static void ext4_free_branches(handle_t *handle, struct inode *inode,
                               struct buffer_head *parent_bh,
                               __le32 *first, __le32 *last, int depth)
{
        ext4_fsblk_t nr;
        __le32 *p;

        if (is_handle_aborted(handle))
                return;

        if (depth--) {
                struct buffer_head *bh;
                int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
                p = last;
                while (--p >= first) {
                        nr = le32_to_cpu(*p);
                        if (!nr)
                                continue;               /* A hole */

                        /* Go read the buffer for the next level down */
                        bh = sb_bread(inode->i_sb, nr);

                        /*
                         * A read failure? Report error and clear slot
                         * (should be rare).
                         */
                        if (!bh) {
                                ext4_error(inode->i_sb, "ext4_free_branches",
                                           "Read failure, inode=%lu, block=%llu",
                                           inode->i_ino, nr);
                                continue;
                        }

                        /* This zaps the entire block.  Bottom up. */
                        BUFFER_TRACE(bh, "free child branches");
                        ext4_free_branches(handle, inode, bh,
                                           (__le32*)bh->b_data,
                                           (__le32*)bh->b_data + addr_per_block,
                                           depth);

                        /*
                         * We've probably journalled the indirect block several
                         * times during the truncate.  But it's no longer
                         * needed and we now drop it from the transaction via
                         * jbd2_journal_revoke().
                         *
                         * That's easy if it's exclusively part of this
                         * transaction.  But if it's part of the committing
                         * transaction then jbd2_journal_forget() will simply
                         * brelse() it.  That means that if the underlying
                         * block is reallocated in ext4_get_block(),
                         * unmap_underlying_metadata() will find this block
                         * and will try to get rid of it.  damn, damn.
                         *
                         * If this block has already been committed to the
                         * journal, a revoke record will be written.  And
                         * revoke records must be emitted *before* clearing
                         * this block's bit in the bitmaps.
                         */
                        ext4_forget(handle, 1, inode, bh, bh->b_blocknr);

                        /*
                         * Everything below this this pointer has been
                         * released.  Now let this top-of-subtree go.
                         *
                         * We want the freeing of this indirect block to be
                         * atomic in the journal with the updating of the
                         * bitmap block which owns it.  So make some room in
                         * the journal.
                         *
                         * We zero the parent pointer *after* freeing its
                         * pointee in the bitmaps, so if extend_transaction()
                         * for some reason fails to put the bitmap changes and
                         * the release into the same transaction, recovery
                         * will merely complain about releasing a free block,
                         * rather than leaking blocks.
                         */
                        if (is_handle_aborted(handle))
                                return;
                        if (try_to_extend_transaction(handle, inode)) {
                                ext4_mark_inode_dirty(handle, inode);
                                ext4_journal_test_restart(handle, inode);
                        }

                        ext4_free_blocks(handle, inode, nr, 1, 1);

                        if (parent_bh) {
                                /*
                                 * The block which we have just freed is
                                 * pointed to by an indirect block: journal it
                                 */
                                BUFFER_TRACE(parent_bh, "get_write_access");
                                if (!ext4_journal_get_write_access(handle,
                                                                   parent_bh)){
                                        *p = 0;
                                        BUFFER_TRACE(parent_bh,
                                        "call ext4_journal_dirty_metadata");
                                        ext4_journal_dirty_metadata(handle,
                                                                    parent_bh);
                                }
                        }
                }
        } else {
                /* We have reached the bottom of the tree. */
                BUFFER_TRACE(parent_bh, "free data blocks");
                ext4_free_data(handle, inode, parent_bh, first, last);
        }
}

int ext4_can_truncate(struct inode *inode)
{
        if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
                return 0;
        if (S_ISREG(inode->i_mode))
                return 1;
        if (S_ISDIR(inode->i_mode))
                return 1;
        if (S_ISLNK(inode->i_mode))
                return !ext4_inode_is_fast_symlink(inode);
        return 0;
}

/*
 * ext4_truncate()
 *
 * We block out ext4_get_block() block instantiations across the entire
 * transaction, and VFS/VM ensures that ext4_truncate() cannot run
 * simultaneously on behalf of the same inode.
 *
 * As we work through the truncate and commmit bits of it to the journal there
 * is one core, guiding principle: the file's tree must always be consistent on
 * disk.  We must be able to restart the truncate after a crash.
 *
 * The file's tree may be transiently inconsistent in memory (although it
 * probably isn't), but whenever we close off and commit a journal transaction,
 * the contents of (the filesystem + the journal) must be consistent and
 * restartable.  It's pretty simple, really: bottom up, right to left (although
 * left-to-right works OK too).
 *
 * Note that at recovery time, journal replay occurs *before* the restart of
 * truncate against the orphan inode list.
 *
 * The committed inode has the new, desired i_size (which is the same as
 * i_disksize in this case).  After a crash, ext4_orphan_cleanup() will see
 * that this inode's truncate did not complete and it will again call
 * ext4_truncate() to have another go.  So there will be instantiated blocks
 * to the right of the truncation point in a crashed ext4 filesystem.  But
 * that's fine - as long as they are linked from the inode, the post-crash
 * ext4_truncate() run will find them and release them.
 */
void ext4_truncate(struct inode *inode)
{
        handle_t *handle;
        struct ext4_inode_info *ei = EXT4_I(inode);
        __le32 *i_data = ei->i_data;
        int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
        struct address_space *mapping = inode->i_mapping;
        ext4_lblk_t offsets[4];
        Indirect chain[4];
        Indirect *partial;
        __le32 nr = 0;
        int n;
        ext4_lblk_t last_block;
        unsigned blocksize = inode->i_sb->s_blocksize;

        if (!ext4_can_truncate(inode))
                return;

        if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
                ext4_ext_truncate(inode);
                return;
        }

        handle = start_transaction(inode);
        if (IS_ERR(handle))
                return;         /* AKPM: return what? */

        last_block = (inode->i_size + blocksize-1)
                                        >> EXT4_BLOCK_SIZE_BITS(inode->i_sb);

        if (inode->i_size & (blocksize - 1))
                if (ext4_block_truncate_page(handle, mapping, inode->i_size))
                        goto out_stop;

        n = ext4_block_to_path(inode, last_block, offsets, NULL);
        if (n == 0)
                goto out_stop;  /* error */

        /*
         * OK.  This truncate is going to happen.  We add the inode to the
         * orphan list, so that if this truncate spans multiple transactions,
         * and we crash, we will resume the truncate when the filesystem
         * recovers.  It also marks the inode dirty, to catch the new size.
         *
         * Implication: the file must always be in a sane, consistent
         * truncatable state while each transaction commits.
         */
        if (ext4_orphan_add(handle, inode))
                goto out_stop;

        /*
         * From here we block out all ext4_get_block() callers who want to
         * modify the block allocation tree.
         */
        down_write(&ei->i_data_sem);

        ext4_discard_reservation(inode);

        /*
         * The orphan list entry will now protect us from any crash which
         * occurs before the truncate completes, so it is now safe to propagate
         * the new, shorter inode size (held for now in i_size) into the
         * on-disk inode. We do this via i_disksize, which is the value which
         * ext4 *really* writes onto the disk inode.
         */
        ei->i_disksize = inode->i_size;

        if (n == 1) {           /* direct blocks */
                ext4_free_data(handle, inode, NULL, i_data+offsets[0],
                               i_data + EXT4_NDIR_BLOCKS);
                goto do_indirects;
        }

        partial = ext4_find_shared(inode, n, offsets, chain, &nr);
        /* Kill the top of shared branch (not detached) */
        if (nr) {
                if (partial == chain) {
                        /* Shared branch grows from the inode */
                        ext4_free_branches(handle, inode, NULL,
                                           &nr, &nr+1, (chain+n-1) - partial);
                        *partial->p = 0;
                        /*
                         * We mark the inode dirty prior to restart,
                         * and prior to stop.  No need for it here.
                         */
                } else {
                        /* Shared branch grows from an indirect block */
                        BUFFER_TRACE(partial->bh, "get_write_access");
                        ext4_free_branches(handle, inode, partial->bh,
                                        partial->p,
                                        partial->p+1, (chain+n-1) - partial);
                }
        }
        /* Clear the ends of indirect blocks on the shared branch */
        while (partial > chain) {
                ext4_free_branches(handle, inode, partial->bh, partial->p + 1,
                                   (__le32*)partial->bh->b_data+addr_per_block,
                                   (chain+n-1) - partial);
                BUFFER_TRACE(partial->bh, "call brelse");
                brelse (partial->bh);
                partial--;
        }
do_indirects:
        /* Kill the remaining (whole) subtrees */
        switch (offsets[0]) {
        default:
                nr = i_data[EXT4_IND_BLOCK];
                if (nr) {
                        ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 1);
                        i_data[EXT4_IND_BLOCK] = 0;
                }
        case EXT4_IND_BLOCK:
                nr = i_data[EXT4_DIND_BLOCK];
                if (nr) {
                        ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 2);
                        i_data[EXT4_DIND_BLOCK] = 0;
                }
        case EXT4_DIND_BLOCK:
                nr = i_data[EXT4_TIND_BLOCK];
                if (nr) {
                        ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 3);
                        i_data[EXT4_TIND_BLOCK] = 0;
                }
        case EXT4_TIND_BLOCK:
                ;
        }

        up_write(&ei->i_data_sem);
        inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
        ext4_mark_inode_dirty(handle, inode);

        /*
         * In a multi-transaction truncate, we only make the final transaction
         * synchronous
         */
        if (IS_SYNC(inode))
                handle->h_sync = 1;
out_stop:
        /*
         * If this was a simple ftruncate(), and the file will remain alive
         * then we need to clear up the orphan record which we created above.
         * However, if this was a real unlink then we were called by
         * ext4_delete_inode(), and we allow that function to clean up the
         * orphan info for us.
         */
        if (inode->i_nlink)
                ext4_orphan_del(handle, inode);

        ext4_journal_stop(handle);
}

static ext4_fsblk_t ext4_get_inode_block(struct super_block *sb,
                unsigned long ino, struct ext4_iloc *iloc)
{
        ext4_group_t block_group;
        unsigned long offset;
        ext4_fsblk_t block;
        struct ext4_group_desc *gdp;

        if (!ext4_valid_inum(sb, ino)) {
                /*
                 * This error is already checked for in namei.c unless we are
                 * looking at an NFS filehandle, in which case no error
                 * report is needed
                 */
                return 0;
        }

        block_group = (ino - 1) / EXT4_INODES_PER_GROUP(sb);
        gdp = ext4_get_group_desc(sb, block_group, NULL);
        if (!gdp)
                return 0;

        /*
         * Figure out the offset within the block group inode table
         */
        offset = ((ino - 1) % EXT4_INODES_PER_GROUP(sb)) *
                EXT4_INODE_SIZE(sb);
        block = ext4_inode_table(sb, gdp) +
                (offset >> EXT4_BLOCK_SIZE_BITS(sb));

        iloc->block_group = block_group;
        iloc->offset = offset & (EXT4_BLOCK_SIZE(sb) - 1);
        return block;
}

/*
 * ext4_get_inode_loc returns with an extra refcount against the inode's
 * underlying buffer_head on success. If 'in_mem' is true, we have all
 * data in memory that is needed to recreate the on-disk version of this
 * inode.
 */
static int __ext4_get_inode_loc(struct inode *inode,
                                struct ext4_iloc *iloc, int in_mem)
{
        ext4_fsblk_t block;
        struct buffer_head *bh;

        block = ext4_get_inode_block(inode->i_sb, inode->i_ino, iloc);
        if (!block)
                return -EIO;

        bh = sb_getblk(inode->i_sb, block);
        if (!bh) {
                ext4_error (inode->i_sb, "ext4_get_inode_loc",
                                "unable to read inode block - "
                                "inode=%lu, block=%llu",
                                 inode->i_ino, block);
                return -EIO;
        }
        if (!buffer_uptodate(bh)) {
                lock_buffer(bh);

                /*
                 * If the buffer has the write error flag, we have failed
                 * to write out another inode in the same block.  In this
                 * case, we don't have to read the block because we may
                 * read the old inode data successfully.
                 */
                if (buffer_write_io_error(bh) && !buffer_uptodate(bh))
                        set_buffer_uptodate(bh);

                if (buffer_uptodate(bh)) {
                        /* someone brought it uptodate while we waited */
                        unlock_buffer(bh);
                        goto has_buffer;
                }

                /*
                 * If we have all information of the inode in memory and this
                 * is the only valid inode in the block, we need not read the
                 * block.
                 */
                if (in_mem) {
                        struct buffer_head *bitmap_bh;
                        struct ext4_group_desc *desc;
                        int inodes_per_buffer;
                        int inode_offset, i;
                        ext4_group_t block_group;
                        int start;

                        block_group = (inode->i_ino - 1) /
                                        EXT4_INODES_PER_GROUP(inode->i_sb);
                        inodes_per_buffer = bh->b_size /
                                EXT4_INODE_SIZE(inode->i_sb);
                        inode_offset = ((inode->i_ino - 1) %
                                        EXT4_INODES_PER_GROUP(inode->i_sb));
                        start = inode_offset & ~(inodes_per_buffer - 1);

                        /* Is the inode bitmap in cache? */
                        desc = ext4_get_group_desc(inode->i_sb,
                                                block_group, NULL);
                        if (!desc)
                                goto make_io;

                        bitmap_bh = sb_getblk(inode->i_sb,
                                ext4_inode_bitmap(inode->i_sb, desc));
                        if (!bitmap_bh)
                                goto make_io;

                        /*
                         * If the inode bitmap isn't in cache then the
                         * optimisation may end up performing two reads instead
                         * of one, so skip it.
                         */
                        if (!buffer_uptodate(bitmap_bh)) {
                                brelse(bitmap_bh);
                                goto make_io;
                        }
                        for (i = start; i < start + inodes_per_buffer; i++) {
                                if (i == inode_offset)
                                        continue;
                                if (ext4_test_bit(i, bitmap_bh->b_data))
                                        break;
                        }
                        brelse(bitmap_bh);
                        if (i == start + inodes_per_buffer) {
                                /* all other inodes are free, so skip I/O */
                                memset(bh->b_data, 0, bh->b_size);
                                set_buffer_uptodate(bh);
                                unlock_buffer(bh);
                                goto has_buffer;
                        }
                }

make_io:
                /*
                 * There are other valid inodes in the buffer, this inode
                 * has in-inode xattrs, or we don't have this inode in memory.
                 * Read the block from disk.
                 */
                get_bh(bh);
                bh->b_end_io = end_buffer_read_sync;
                submit_bh(READ_META, bh);
                wait_on_buffer(bh);
                if (!buffer_uptodate(bh)) {
                        ext4_error(inode->i_sb, "ext4_get_inode_loc",
                                        "unable to read inode block - "
                                        "inode=%lu, block=%llu",
                                        inode->i_ino, block);
                        brelse(bh);
                        return -EIO;
                }
        }
has_buffer:
        iloc->bh = bh;
        return 0;
}

int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc)
{
        /* We have all inode data except xattrs in memory here. */
        return __ext4_get_inode_loc(inode, iloc,
                !(EXT4_I(inode)->i_state & EXT4_STATE_XATTR));
}

void ext4_set_inode_flags(struct inode *inode)
{
        unsigned int flags = EXT4_I(inode)->i_flags;

        inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
        if (flags & EXT4_SYNC_FL)
                inode->i_flags |= S_SYNC;
        if (flags & EXT4_APPEND_FL)
                inode->i_flags |= S_APPEND;
        if (flags & EXT4_IMMUTABLE_FL)
                inode->i_flags |= S_IMMUTABLE;
        if (flags & EXT4_NOATIME_FL)
                inode->i_flags |= S_NOATIME;
        if (flags & EXT4_DIRSYNC_FL)
                inode->i_flags |= S_DIRSYNC;
}

/* Propagate flags from i_flags to EXT4_I(inode)->i_flags */
void ext4_get_inode_flags(struct ext4_inode_info *ei)
{
        unsigned int flags = ei->vfs_inode.i_flags;

        ei->i_flags &= ~(EXT4_SYNC_FL|EXT4_APPEND_FL|
                        EXT4_IMMUTABLE_FL|EXT4_NOATIME_FL|EXT4_DIRSYNC_FL);
        if (flags & S_SYNC)
                ei->i_flags |= EXT4_SYNC_FL;
        if (flags & S_APPEND)
                ei->i_flags |= EXT4_APPEND_FL;
        if (flags & S_IMMUTABLE)
                ei->i_flags |= EXT4_IMMUTABLE_FL;
        if (flags & S_NOATIME)
                ei->i_flags |= EXT4_NOATIME_FL;
        if (flags & S_DIRSYNC)
                ei->i_flags |= EXT4_DIRSYNC_FL;
}
static blkcnt_t ext4_inode_blocks(struct ext4_inode *raw_inode,
                                        struct ext4_inode_info *ei)
{
        blkcnt_t i_blocks ;
        struct inode *inode = &(ei->vfs_inode);
        struct super_block *sb = inode->i_sb;

        if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
                                EXT4_FEATURE_RO_COMPAT_HUGE_FILE)) {
                /* we are using combined 48 bit field */
                i_blocks = ((u64)le16_to_cpu(raw_inode->i_blocks_high)) << 32 |
                                        le32_to_cpu(raw_inode->i_blocks_lo);
                if (ei->i_flags & EXT4_HUGE_FILE_FL) {
                        /* i_blocks represent file system block size */
                        return i_blocks  << (inode->i_blkbits - 9);
                } else {
                        return i_blocks;
                }
        } else {
                return le32_to_cpu(raw_inode->i_blocks_lo);
        }
}

struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
{
        struct ext4_iloc iloc;
        struct ext4_inode *raw_inode;
        struct ext4_inode_info *ei;
        struct buffer_head *bh;
        struct inode *inode;
        long ret;
        int block;

        inode = iget_locked(sb, ino);
        if (!inode)
                return ERR_PTR(-ENOMEM);
        if (!(inode->i_state & I_NEW))
                return inode;

        ei = EXT4_I(inode);
#ifdef CONFIG_EXT4DEV_FS_POSIX_ACL
        ei->i_acl = EXT4_ACL_NOT_CACHED;
        ei->i_default_acl = EXT4_ACL_NOT_CACHED;
#endif
        ei->i_block_alloc_info = NULL;

        ret = __ext4_get_inode_loc(inode, &iloc, 0);
        if (ret < 0)
                goto bad_inode;
        bh = iloc.bh;
        raw_inode = ext4_raw_inode(&iloc);
        inode->i_mode = le16_to_cpu(raw_inode->i_mode);
        inode->i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
        inode->i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
        if(!(test_opt (inode->i_sb, NO_UID32))) {
                inode->i_uid |= le16_to_cpu(raw_inode->i_uid_high) << 16;
                inode->i_gid |= le16_to_cpu(raw_inode->i_gid_high) << 16;
        }
        inode->i_nlink = le16_to_cpu(raw_inode->i_links_count);

        ei->i_state = 0;
        ei->i_dir_start_lookup = 0;
        ei->i_dtime = le32_to_cpu(raw_inode->i_dtime);
        /* We now have enough fields to check if the inode was active or not.
         * This is needed because nfsd might try to access dead inodes
         * the test is that same one that e2fsck uses
         * NeilBrown 1999oct15
         */
        if (inode->i_nlink == 0) {
                if (inode->i_mode == 0 ||
                    !(EXT4_SB(inode->i_sb)->s_mount_state & EXT4_ORPHAN_FS)) {
                        /* this inode is deleted */
                        brelse (bh);
                        ret = -ESTALE;
                        goto bad_inode;
                }
                /* The only unlinked inodes we let through here have
                 * valid i_mode and are being read by the orphan
                 * recovery code: that's fine, we're about to complete
                 * the process of deleting those. */
        }
        ei->i_flags = le32_to_cpu(raw_inode->i_flags);
        inode->i_blocks = ext4_inode_blocks(raw_inode, ei);
        ei->i_file_acl = le32_to_cpu(raw_inode->i_file_acl_lo);
        if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
            cpu_to_le32(EXT4_OS_HURD)) {
                ei->i_file_acl |=
                        ((__u64)le16_to_cpu(raw_inode->i_file_acl_high)) << 32;
        }
        inode->i_size = ext4_isize(raw_inode);
        ei->i_disksize = inode->i_size;
        inode->i_generation = le32_to_cpu(raw_inode->i_generation);
        ei->i_block_group = iloc.block_group;
        /*
         * NOTE! The in-memory inode i_data array is in little-endian order
         * even on big-endian machines: we do NOT byteswap the block numbers!
         */
        for (block = 0; block < EXT4_N_BLOCKS; block++)
                ei->i_data[block] = raw_inode->i_block[block];
        INIT_LIST_HEAD(&ei->i_orphan);

        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
                ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize);
                if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize >
                    EXT4_INODE_SIZE(inode->i_sb)) {
                        brelse (bh);
                        ret = -EIO;
                        goto bad_inode;
                }
                if (ei->i_extra_isize == 0) {
                        /* The extra space is currently unused. Use it. */
                        ei->i_extra_isize = sizeof(struct ext4_inode) -
                                            EXT4_GOOD_OLD_INODE_SIZE;
                } else {
                        __le32 *magic = (void *)raw_inode +
                                        EXT4_GOOD_OLD_INODE_SIZE +
                                        ei->i_extra_isize;
                        if (*magic == cpu_to_le32(EXT4_XATTR_MAGIC))
                                 ei->i_state |= EXT4_STATE_XATTR;
                }
        } else
                ei->i_extra_isize = 0;

        EXT4_INODE_GET_XTIME(i_ctime, inode, raw_inode);
        EXT4_INODE_GET_XTIME(i_mtime, inode, raw_inode);
        EXT4_INODE_GET_XTIME(i_atime, inode, raw_inode);
        EXT4_EINODE_GET_XTIME(i_crtime, ei, raw_inode);

        inode->i_version = le32_to_cpu(raw_inode->i_disk_version);
        if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
                if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
                        inode->i_version |=
                        (__u64)(le32_to_cpu(raw_inode->i_version_hi)) << 32;
        }

        if (S_ISREG(inode->i_mode)) {
                inode->i_op = &ext4_file_inode_operations;
                inode->i_fop = &ext4_file_operations;
                ext4_set_aops(inode);
        } else if (S_ISDIR(inode->i_mode)) {
                inode->i_op = &ext4_dir_inode_operations;
                inode->i_fop = &ext4_dir_operations;
        } else if (S_ISLNK(inode->i_mode)) {
                if (ext4_inode_is_fast_symlink(inode))
                        inode->i_op = &ext4_fast_symlink_inode_operations;
                else {
                        inode->i_op = &ext4_symlink_inode_operations;
                        ext4_set_aops(inode);
                }
        } else {
                inode->i_op = &ext4_special_inode_operations;
                if (raw_inode->i_block[0])
                        init_special_inode(inode, inode->i_mode,
                           old_decode_dev(le32_to_cpu(raw_inode->i_block[0])));
                else
                        init_special_inode(inode, inode->i_mode,
                           new_decode_dev(le32_to_cpu(raw_inode->i_block[1])));
        }
        brelse (iloc.bh);
        ext4_set_inode_flags(inode);
        unlock_new_inode(inode);
        return inode;

bad_inode:
        iget_failed(inode);
        return ERR_PTR(ret);
}

static int ext4_inode_blocks_set(handle_t *handle,
                                struct ext4_inode *raw_inode,
                                struct ext4_inode_info *ei)
{
        struct inode *inode = &(ei->vfs_inode);
        u64 i_blocks = inode->i_blocks;
        struct super_block *sb = inode->i_sb;
        int err = 0;

        if (i_blocks <= ~0U) {
                /*
                 * i_blocks can be represnted in a 32 bit variable
                 * as multiple of 512 bytes
                 */
                raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
                raw_inode->i_blocks_high = 0;
                ei->i_flags &= ~EXT4_HUGE_FILE_FL;
        } else if (i_blocks <= 0xffffffffffffULL) {
                /*
                 * i_blocks can be represented in a 48 bit variable
                 * as multiple of 512 bytes
                 */
                err = ext4_update_rocompat_feature(handle, sb,
                                            EXT4_FEATURE_RO_COMPAT_HUGE_FILE);
                if (err)
                        goto  err_out;
                /* i_block is stored in the split  48 bit fields */
                raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
                raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
                ei->i_flags &= ~EXT4_HUGE_FILE_FL;
        } else {
                /*
                 * i_blocks should be represented in a 48 bit variable
                 * as multiple of  file system block size
                 */
                err = ext4_update_rocompat_feature(handle, sb,
                                            EXT4_FEATURE_RO_COMPAT_HUGE_FILE);
                if (err)
                        goto  err_out;
                ei->i_flags |= EXT4_HUGE_FILE_FL;
                /* i_block is stored in file system block size */
                i_blocks = i_blocks >> (inode->i_blkbits - 9);
                raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
                raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
        }
err_out:
        return err;
}

/*
 * Post the struct inode info into an on-disk inode location in the
 * buffer-cache.  This gobbles the caller's reference to the
 * buffer_head in the inode location struct.
 *
 * The caller must have write access to iloc->bh.
 */
static int ext4_do_update_inode(handle_t *handle,
                                struct inode *inode,
                                struct ext4_iloc *iloc)
{
        struct ext4_inode *raw_inode = ext4_raw_inode(iloc);
        struct ext4_inode_info *ei = EXT4_I(inode);
        struct buffer_head *bh = iloc->bh;
        int err = 0, rc, block;

        /* For fields not not tracking in the in-memory inode,
         * initialise them to zero for new inodes. */
        if (ei->i_state & EXT4_STATE_NEW)
                memset(raw_inode, 0, EXT4_SB(inode->i_sb)->s_inode_size);

        ext4_get_inode_flags(ei);
        raw_inode->i_mode = cpu_to_le16(inode->i_mode);
        if(!(test_opt(inode->i_sb, NO_UID32))) {
                raw_inode->i_uid_low = cpu_to_le16(low_16_bits(inode->i_uid));
                raw_inode->i_gid_low = cpu_to_le16(low_16_bits(inode->i_gid));
/*
 * Fix up interoperability with old kernels. Otherwise, old inodes get
 * re-used with the upper 16 bits of the uid/gid intact
 */
                if(!ei->i_dtime) {
                        raw_inode->i_uid_high =
                                cpu_to_le16(high_16_bits(inode->i_uid));
                        raw_inode->i_gid_high =
                                cpu_to_le16(high_16_bits(inode->i_gid));
                } else {
                        raw_inode->i_uid_high = 0;
                        raw_inode->i_gid_high = 0;
                }
        } else {
                raw_inode->i_uid_low =
                        cpu_to_le16(fs_high2lowuid(inode->i_uid));
                raw_inode->i_gid_low =
                        cpu_to_le16(fs_high2lowgid(inode->i_gid));
                raw_inode->i_uid_high = 0;
                raw_inode->i_gid_high = 0;
        }
        raw_inode->i_links_count = cpu_to_le16(inode->i_nlink);

        EXT4_INODE_SET_XTIME(i_ctime, inode, raw_inode);
        EXT4_INODE_SET_XTIME(i_mtime, inode, raw_inode);
        EXT4_INODE_SET_XTIME(i_atime, inode, raw_inode);
        EXT4_EINODE_SET_XTIME(i_crtime, ei, raw_inode);

        if (ext4_inode_blocks_set(handle, raw_inode, ei))
                goto out_brelse;
        raw_inode->i_dtime = cpu_to_le32(ei->i_dtime);
        /* clear the migrate flag in the raw_inode */
        raw_inode->i_flags = cpu_to_le32(ei->i_flags & ~EXT4_EXT_MIGRATE);
        if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
            cpu_to_le32(EXT4_OS_HURD))
                raw_inode->i_file_acl_high =
                        cpu_to_le16(ei->i_file_acl >> 32);
        raw_inode->i_file_acl_lo = cpu_to_le32(ei->i_file_acl);
        ext4_isize_set(raw_inode, ei->i_disksize);
        if (ei->i_disksize > 0x7fffffffULL) {
                struct super_block *sb = inode->i_sb;
                if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
                                EXT4_FEATURE_RO_COMPAT_LARGE_FILE) ||
                                EXT4_SB(sb)->s_es->s_rev_level ==
                                cpu_to_le32(EXT4_GOOD_OLD_REV)) {
                        /* If this is the first large file
                         * created, add a flag to the superblock.
                         */
                        err = ext4_journal_get_write_access(handle,
                                        EXT4_SB(sb)->s_sbh);
                        if (err)
                                goto out_brelse;
                        ext4_update_dynamic_rev(sb);
                        EXT4_SET_RO_COMPAT_FEATURE(sb,
                                        EXT4_FEATURE_RO_COMPAT_LARGE_FILE);
                        sb->s_dirt = 1;
                        handle->h_sync = 1;
                        err = ext4_journal_dirty_metadata(handle,
                                        EXT4_SB(sb)->s_sbh);
                }
        }
        raw_inode->i_generation = cpu_to_le32(inode->i_generation);
        if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode)) {
                if (old_valid_dev(inode->i_rdev)) {
                        raw_inode->i_block[0] =
                                cpu_to_le32(old_encode_dev(inode->i_rdev));
                        raw_inode->i_block[1] = 0;
                } else {
                        raw_inode->i_block[0] = 0;
                        raw_inode->i_block[1] =
                                cpu_to_le32(new_encode_dev(inode->i_rdev));
                        raw_inode->i_block[2] = 0;
                }
        } else for (block = 0; block < EXT4_N_BLOCKS; block++)
                raw_inode->i_block[block] = ei->i_data[block];

        raw_inode->i_disk_version = cpu_to_le32(inode->i_version);
        if (ei->i_extra_isize) {
                if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
                        raw_inode->i_version_hi =
                        cpu_to_le32(inode->i_version >> 32);
                raw_inode->i_extra_isize = cpu_to_le16(ei->i_extra_isize);
        }


        BUFFER_TRACE(bh, "call ext4_journal_dirty_metadata");
        rc = ext4_journal_dirty_metadata(handle, bh);
        if (!err)
                err = rc;
        ei->i_state &= ~EXT4_STATE_NEW;

out_brelse:
        brelse (bh);
        ext4_std_error(inode->i_sb, err);
        return err;
}

/*
 * ext4_write_inode()
 *
 * We are called from a few places:
 *
 * - Within generic_file_write() for O_SYNC files.
 *   Here, there will be no transaction running. We wait for any running
 *   trasnaction to commit.
 *
 * - Within sys_sync(), kupdate and such.
 *   We wait on commit, if tol to.
 *
 * - Within prune_icache() (PF_MEMALLOC == true)
 *   Here we simply return.  We can't afford to block kswapd on the
 *   journal commit.
 *
 * In all cases it is actually safe for us to return without doing anything,
 * because the inode has been copied into a raw inode buffer in
 * ext4_mark_inode_dirty().  This is a correctness thing for O_SYNC and for
 * knfsd.
 *
 * Note that we are absolutely dependent upon all inode dirtiers doing the
 * right thing: they *must* call mark_inode_dirty() after dirtying info in
 * which we are interested.
 *
 * It would be a bug for them to not do this.  The code:
 *
 *      mark_inode_dirty(inode)
 *      stuff();
 *      inode->i_size = expr;
 *
 * is in error because a kswapd-driven write_inode() could occur while
 * `stuff()' is running, and the new i_size will be lost.  Plus the inode
 * will no longer be on the superblock's dirty inode list.
 */
int ext4_write_inode(struct inode *inode, int wait)
{
        if (current->flags & PF_MEMALLOC)
                return 0;

        if (ext4_journal_current_handle()) {
                jbd_debug(1, "called recursively, non-PF_MEMALLOC!\n");
                dump_stack();
                return -EIO;
        }

        if (!wait)
                return 0;

        return ext4_force_commit(inode->i_sb);
}

/*
 * ext4_setattr()
 *
 * Called from notify_change.
 *
 * We want to trap VFS attempts to truncate the file as soon as
 * possible.  In particular, we want to make sure that when the VFS
 * shrinks i_size, we put the inode on the orphan list and modify
 * i_disksize immediately, so that during the subsequent flushing of
 * dirty pages and freeing of disk blocks, we can guarantee that any
 * commit will leave the blocks being flushed in an unused state on
 * disk.  (On recovery, the inode will get truncated and the blocks will
 * be freed, so we have a strong guarantee that no future commit will
 * leave these blocks visible to the user.)
 *
 * Another thing we have to assure is that if we are in ordered mode
 * and inode is still attached to the committing transaction, we must
 * we start writeout of all the dirty pages which are being truncated.
 * This way we are sure that all the data written in the previous
 * transaction are already on disk (truncate waits for pages under
 * writeback).
 *
 * Called with inode->i_mutex down.
 */
int ext4_setattr(struct dentry *dentry, struct iattr *attr)
{
        struct inode *inode = dentry->d_inode;
        int error, rc = 0;
        const unsigned int ia_valid = attr->ia_valid;

        error = inode_change_ok(inode, attr);
        if (error)
                return error;

        if ((ia_valid & ATTR_UID && attr->ia_uid != inode->i_uid) ||
                (ia_valid & ATTR_GID && attr->ia_gid != inode->i_gid)) {
                handle_t *handle;

                /* (user+group)*(old+new) structure, inode write (sb,
                 * inode block, ? - but truncate inode update has it) */
                handle = ext4_journal_start(inode, 2*(EXT4_QUOTA_INIT_BLOCKS(inode->i_sb)+
                                        EXT4_QUOTA_DEL_BLOCKS(inode->i_sb))+3);
                if (IS_ERR(handle)) {
                        error = PTR_ERR(handle);
                        goto err_out;
                }
                error = DQUOT_TRANSFER(inode, attr) ? -EDQUOT : 0;
                if (error) {
                        ext4_journal_stop(handle);
                        return error;
                }
                /* Update corresponding info in inode so that everything is in
                 * one transaction */
                if (attr->ia_valid & ATTR_UID)
                        inode->i_uid = attr->ia_uid;
                if (attr->ia_valid & ATTR_GID)
                        inode->i_gid = attr->ia_gid;
                error = ext4_mark_inode_dirty(handle, inode);
                ext4_journal_stop(handle);
        }

        if (attr->ia_valid & ATTR_SIZE) {
                if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL)) {
                        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);

                        if (attr->ia_size > sbi->s_bitmap_maxbytes) {
                                error = -EFBIG;
                                goto err_out;
                        }
                }
        }

        if (S_ISREG(inode->i_mode) &&
            attr->ia_valid & ATTR_SIZE && attr->ia_size < inode->i_size) {
                handle_t *handle;

                handle = ext4_journal_start(inode, 3);
                if (IS_ERR(handle)) {
                        error = PTR_ERR(handle);
                        goto err_out;
                }

                error = ext4_orphan_add(handle, inode);
                EXT4_I(inode)->i_disksize = attr->ia_size;
                rc = ext4_mark_inode_dirty(handle, inode);
                if (!error)
                        error = rc;
                ext4_journal_stop(handle);

                if (ext4_should_order_data(inode)) {
                        error = ext4_begin_ordered_truncate(inode,
                                                            attr->ia_size);
                        if (error) {
                                /* Do as much error cleanup as possible */
                                handle = ext4_journal_start(inode, 3);
                                if (IS_ERR(handle)) {
                                        ext4_orphan_del(NULL, inode);
                                        goto err_out;
                                }
                                ext4_orphan_del(handle, inode);
                                ext4_journal_stop(handle);
                                goto err_out;
                        }
                }
        }

        rc = inode_setattr(inode, attr);

        /* If inode_setattr's call to ext4_truncate failed to get a
         * transaction handle at all, we need to clean up the in-core
         * orphan list manually. */
        if (inode->i_nlink)
                ext4_orphan_del(NULL, inode);

        if (!rc && (ia_valid & ATTR_MODE))
                rc = ext4_acl_chmod(inode);

err_out:
        ext4_std_error(inode->i_sb, error);
        if (!error)
                error = rc;
        return error;
}

int ext4_getattr(struct vfsmount *mnt, struct dentry *dentry,
                 struct kstat *stat)
{
        struct inode *inode;
        unsigned long delalloc_blocks;

        inode = dentry->d_inode;
        generic_fillattr(inode, stat);

        /*
         * We can't update i_blocks if the block allocation is delayed
         * otherwise in the case of system crash before the real block
         * allocation is done, we will have i_blocks inconsistent with
         * on-disk file blocks.
         * We always keep i_blocks updated together with real
         * allocation. But to not confuse with user, stat
         * will return the blocks that include the delayed allocation
         * blocks for this file.
         */
        spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
        delalloc_blocks = EXT4_I(inode)->i_reserved_data_blocks;
        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);

        stat->blocks += (delalloc_blocks << inode->i_sb->s_blocksize_bits)>>9;
        return 0;
}

static int ext4_indirect_trans_blocks(struct inode *inode, int nrblocks,
                                      int chunk)
{
        int indirects;

        /* if nrblocks are contiguous */
        if (chunk) {
                /*
                 * With N contiguous data blocks, it need at most
                 * N/EXT4_ADDR_PER_BLOCK(inode->i_sb) indirect blocks
                 * 2 dindirect blocks
                 * 1 tindirect block
                 */
                indirects = nrblocks / EXT4_ADDR_PER_BLOCK(inode->i_sb);
                return indirects + 3;
        }
        /*
         * if nrblocks are not contiguous, worse case, each block touch
         * a indirect block, and each indirect block touch a double indirect
         * block, plus a triple indirect block
         */
        indirects = nrblocks * 2 + 1;
        return indirects;
}

static int ext4_index_trans_blocks(struct inode *inode, int nrblocks, int chunk)
{
        if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
                return ext4_indirect_trans_blocks(inode, nrblocks, 0);
        return ext4_ext_index_trans_blocks(inode, nrblocks, 0);
}
/*
 * Account for index blocks, block groups bitmaps and block group
 * descriptor blocks if modify datablocks and index blocks
 * worse case, the indexs blocks spread over different block groups
 *
 * If datablocks are discontiguous, they are possible to spread over
 * different block groups too. If they are contiugous, with flexbg,
 * they could still across block group boundary.
 *
 * Also account for superblock, inode, quota and xattr blocks
 */
int ext4_meta_trans_blocks(struct inode *inode, int nrblocks, int chunk)
{
        int groups, gdpblocks;
        int idxblocks;
        int ret = 0;

        /*
         * How many index blocks need to touch to modify nrblocks?
         * The "Chunk" flag indicating whether the nrblocks is
         * physically contiguous on disk
         *
         * For Direct IO and fallocate, they calls get_block to allocate
         * one single extent at a time, so they could set the "Chunk" flag
         */
        idxblocks = ext4_index_trans_blocks(inode, nrblocks, chunk);

        ret = idxblocks;

        /*
         * Now let's see how many group bitmaps and group descriptors need
         * to account
         */
        groups = idxblocks;
        if (chunk)
                groups += 1;
        else
                groups += nrblocks;

        gdpblocks = groups;
        if (groups > EXT4_SB(inode->i_sb)->s_groups_count)
                groups = EXT4_SB(inode->i_sb)->s_groups_count;
        if (groups > EXT4_SB(inode->i_sb)->s_gdb_count)
                gdpblocks = EXT4_SB(inode->i_sb)->s_gdb_count;

        /* bitmaps and block group descriptor blocks */
        ret += groups + gdpblocks;

        /* Blocks for super block, inode, quota and xattr blocks */
        ret += EXT4_META_TRANS_BLOCKS(inode->i_sb);

        return ret;
}

/*
 * Calulate the total number of credits to reserve to fit
 * the modification of a single pages into a single transaction,
 * which may include multiple chunks of block allocations.
 *
 * This could be called via ext4_write_begin()
 *
 * We need to consider the worse case, when
 * one new block per extent.
 */
int ext4_writepage_trans_blocks(struct inode *inode)
{
        int bpp = ext4_journal_blocks_per_page(inode);
        int ret;

        ret = ext4_meta_trans_blocks(inode, bpp, 0);

        /* Account for data blocks for journalled mode */
        if (ext4_should_journal_data(inode))
                ret += bpp;
        return ret;
}

/*
 * Calculate the journal credits for a chunk of data modification.
 *
 * This is called from DIO, fallocate or whoever calling
 * ext4_get_blocks_wrap() to map/allocate a chunk of contigous disk blocks.
 *
 * journal buffers for data blocks are not included here, as DIO
 * and fallocate do no need to journal data buffers.
 */
int ext4_chunk_trans_blocks(struct inode *inode, int nrblocks)
{
        return ext4_meta_trans_blocks(inode, nrblocks, 1);
}

/*
 * The caller must have previously called ext4_reserve_inode_write().
 * Give this, we know that the caller already has write access to iloc->bh.
 */
int ext4_mark_iloc_dirty(handle_t *handle,
                struct inode *inode, struct ext4_iloc *iloc)
{
        int err = 0;

        if (test_opt(inode->i_sb, I_VERSION))
                inode_inc_iversion(inode);

        /* the do_update_inode consumes one bh->b_count */
        get_bh(iloc->bh);

        /* ext4_do_update_inode() does jbd2_journal_dirty_metadata */
        err = ext4_do_update_inode(handle, inode, iloc);
        put_bh(iloc->bh);
        return err;
}

/*
 * On success, We end up with an outstanding reference count against
 * iloc->bh.  This _must_ be cleaned up later.
 */

int
ext4_reserve_inode_write(handle_t *handle, struct inode *inode,
                         struct ext4_iloc *iloc)
{
        int err = 0;
        if (handle) {
                err = ext4_get_inode_loc(inode, iloc);
                if (!err) {
                        BUFFER_TRACE(iloc->bh, "get_write_access");
                        err = ext4_journal_get_write_access(handle, iloc->bh);
                        if (err) {
                                brelse(iloc->bh);
                                iloc->bh = NULL;
                        }
                }
        }
        ext4_std_error(inode->i_sb, err);
        return err;
}

/*
 * Expand an inode by new_extra_isize bytes.
 * Returns 0 on success or negative error number on failure.
 */
static int ext4_expand_extra_isize(struct inode *inode,
                                   unsigned int new_extra_isize,
                                   struct ext4_iloc iloc,
                                   handle_t *handle)
{
        struct ext4_inode *raw_inode;
        struct ext4_xattr_ibody_header *header;
        struct ext4_xattr_entry *entry;

        if (EXT4_I(inode)->i_extra_isize >= new_extra_isize)
                return 0;

        raw_inode = ext4_raw_inode(&iloc);

        header = IHDR(inode, raw_inode);
        entry = IFIRST(header);

        /* No extended attributes present */
        if (!(EXT4_I(inode)->i_state & EXT4_STATE_XATTR) ||
                header->h_magic != cpu_to_le32(EXT4_XATTR_MAGIC)) {
                memset((void *)raw_inode + EXT4_GOOD_OLD_INODE_SIZE, 0,
                        new_extra_isize);
                EXT4_I(inode)->i_extra_isize = new_extra_isize;
                return 0;
        }

        /* try to expand with EAs present */
        return ext4_expand_extra_isize_ea(inode, new_extra_isize,
                                          raw_inode, handle);
}

/*
 * What we do here is to mark the in-core inode as clean with respect to inode
 * dirtiness (it may still be data-dirty).
 * This means that the in-core inode may be reaped by prune_icache
 * without having to perform any I/O.  This is a very good thing,
 * because *any* task may call prune_icache - even ones which
 * have a transaction open against a different journal.
 *
 * Is this cheating?  Not really.  Sure, we haven't written the
 * inode out, but prune_icache isn't a user-visible syncing function.
 * Whenever the user wants stuff synced (sys_sync, sys_msync, sys_fsync)
 * we start and wait on commits.
 *
 * Is this efficient/effective?  Well, we're being nice to the system
 * by cleaning up our inodes proactively so they can be reaped
 * without I/O.  But we are potentially leaving up to five seconds'
 * worth of inodes floating about which prune_icache wants us to
 * write out.  One way to fix that would be to get prune_icache()
 * to do a write_super() to free up some memory.  It has the desired
 * effect.
 */
int ext4_mark_inode_dirty(handle_t *handle, struct inode *inode)
{
        struct ext4_iloc iloc;
        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
        static unsigned int mnt_count;
        int err, ret;

        might_sleep();
        err = ext4_reserve_inode_write(handle, inode, &iloc);
        if (EXT4_I(inode)->i_extra_isize < sbi->s_want_extra_isize &&
            !(EXT4_I(inode)->i_state & EXT4_STATE_NO_EXPAND)) {
                /*
                 * We need extra buffer credits since we may write into EA block
                 * with this same handle. If journal_extend fails, then it will
                 * only result in a minor loss of functionality for that inode.
                 * If this is felt to be critical, then e2fsck should be run to
                 * force a large enough s_min_extra_isize.
                 */
                if ((jbd2_journal_extend(handle,
                             EXT4_DATA_TRANS_BLOCKS(inode->i_sb))) == 0) {
                        ret = ext4_expand_extra_isize(inode,
                                                      sbi->s_want_extra_isize,
                                                      iloc, handle);
                        if (ret) {
                                EXT4_I(inode)->i_state |= EXT4_STATE_NO_EXPAND;
                                if (mnt_count !=
                                        le16_to_cpu(sbi->s_es->s_mnt_count)) {
                                        ext4_warning(inode->i_sb, __func__,
                                        "Unable to expand inode %lu. Delete"
                                        " some EAs or run e2fsck.",
                                        inode->i_ino);
                                        mnt_count =
                                          le16_to_cpu(sbi->s_es->s_mnt_count);
                                }
                        }
                }
        }
        if (!err)
                err = ext4_mark_iloc_dirty(handle, inode, &iloc);
        return err;
}

/*
 * ext4_dirty_inode() is called from __mark_inode_dirty()
 *
 * We're really interested in the case where a file is being extended.
 * i_size has been changed by generic_commit_write() and we thus need
 * to include the updated inode in the current transaction.
 *
 * Also, DQUOT_ALLOC_SPACE() will always dirty the inode when blocks
 * are allocated to the file.
 *
 * If the inode is marked synchronous, we don't honour that here - doing
 * so would cause a commit on atime updates, which we don't bother doing.
 * We handle synchronous inodes at the highest possible level.
 */
void ext4_dirty_inode(struct inode *inode)
{
        handle_t *current_handle = ext4_journal_current_handle();
        handle_t *handle;

        handle = ext4_journal_start(inode, 2);
        if (IS_ERR(handle))
                goto out;
        if (current_handle &&
                current_handle->h_transaction != handle->h_transaction) {
                /* This task has a transaction open against a different fs */
                printk(KERN_EMERG "%s: transactions do not match!\n",
                       __func__);
        } else {
                jbd_debug(5, "marking dirty.  outer handle=%p\n",
                                current_handle);
                ext4_mark_inode_dirty(handle, inode);
        }
        ext4_journal_stop(handle);
out:
        return;
}

#if 0
/*
 * Bind an inode's backing buffer_head into this transaction, to prevent
 * it from being flushed to disk early.  Unlike
 * ext4_reserve_inode_write, this leaves behind no bh reference and
 * returns no iloc structure, so the caller needs to repeat the iloc
 * lookup to mark the inode dirty later.
 */
static int ext4_pin_inode(handle_t *handle, struct inode *inode)
{
        struct ext4_iloc iloc;

        int err = 0;
        if (handle) {
                err = ext4_get_inode_loc(inode, &iloc);
                if (!err) {
                        BUFFER_TRACE(iloc.bh, "get_write_access");
                        err = jbd2_journal_get_write_access(handle, iloc.bh);
                        if (!err)
                                err = ext4_journal_dirty_metadata(handle,
                                                                  iloc.bh);
                        brelse(iloc.bh);
                }
        }
        ext4_std_error(inode->i_sb, err);
        return err;
}
#endif

int ext4_change_inode_journal_flag(struct inode *inode, int val)
{
        journal_t *journal;
        handle_t *handle;
        int err;

        /*
         * We have to be very careful here: changing a data block's
         * journaling status dynamically is dangerous.  If we write a
         * data block to the journal, change the status and then delete
         * that block, we risk forgetting to revoke the old log record
         * from the journal and so a subsequent replay can corrupt data.
         * So, first we make sure that the journal is empty and that
         * nobody is changing anything.
         */

        journal = EXT4_JOURNAL(inode);
        if (is_journal_aborted(journal))
                return -EROFS;

        jbd2_journal_lock_updates(journal);
        jbd2_journal_flush(journal);

        /*
         * OK, there are no updates running now, and all cached data is
         * synced to disk.  We are now in a completely consistent state
         * which doesn't have anything in the journal, and we know that
         * no filesystem updates are running, so it is safe to modify
         * the inode's in-core data-journaling state flag now.
         */

        if (val)
                EXT4_I(inode)->i_flags |= EXT4_JOURNAL_DATA_FL;
        else
                EXT4_I(inode)->i_flags &= ~EXT4_JOURNAL_DATA_FL;
        ext4_set_aops(inode);

        jbd2_journal_unlock_updates(journal);

        /* Finally we can mark the inode as dirty. */

        handle = ext4_journal_start(inode, 1);
        if (IS_ERR(handle))
                return PTR_ERR(handle);

        err = ext4_mark_inode_dirty(handle, inode);
        handle->h_sync = 1;
        ext4_journal_stop(handle);
        ext4_std_error(inode->i_sb, err);

        return err;
}

static int ext4_bh_unmapped(handle_t *handle, struct buffer_head *bh)
{
        return !buffer_mapped(bh);
}

int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page)
{
        loff_t size;
        unsigned long len;
        int ret = -EINVAL;
        struct file *file = vma->vm_file;
        struct inode *inode = file->f_path.dentry->d_inode;
        struct address_space *mapping = inode->i_mapping;

        /*
         * Get i_alloc_sem to stop truncates messing with the inode. We cannot
         * get i_mutex because we are already holding mmap_sem.
         */
        down_read(&inode->i_alloc_sem);
        size = i_size_read(inode);
        if (page->mapping != mapping || size <= page_offset(page)
            || !PageUptodate(page)) {
                /* page got truncated from under us? */
                goto out_unlock;
        }
        ret = 0;
        if (PageMappedToDisk(page))
                goto out_unlock;

        if (page->index == size >> PAGE_CACHE_SHIFT)
                len = size & ~PAGE_CACHE_MASK;
        else
                len = PAGE_CACHE_SIZE;

        if (page_has_buffers(page)) {
                /* return if we have all the buffers mapped */
                if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
                                       ext4_bh_unmapped))
                        goto out_unlock;
        }
        /*
         * OK, we need to fill the hole... Do write_begin write_end
         * to do block allocation/reservation.We are not holding
         * inode.i__mutex here. That allow * parallel write_begin,
         * write_end call. lock_page prevent this from happening
         * on the same page though
         */
        ret = mapping->a_ops->write_begin(file, mapping, page_offset(page),
                        len, AOP_FLAG_UNINTERRUPTIBLE, &page, NULL);
        if (ret < 0)
                goto out_unlock;
        ret = mapping->a_ops->write_end(file, mapping, page_offset(page),
                        len, len, page, NULL);
        if (ret < 0)
                goto out_unlock;
        ret = 0;
out_unlock:
        up_read(&inode->i_alloc_sem);
        return ret;
}