Original author: Richard Gooch <rgooch@atnf.csiro.au>
- Last updated on October 28, 2005
+ Last updated on June 24, 2007.
Copyright (C) 1999 Richard Gooch
Copyright (C) 2005 Pekka Enberg
struct file_system_type
-----------------------
-This describes the filesystem. As of kernel 2.6.13, the following
+This describes the filesystem. As of kernel 2.6.22, the following
members are defined:
struct file_system_type {
struct module *owner;
struct file_system_type * next;
struct list_head fs_supers;
+ struct lock_class_key s_lock_key;
+ struct lock_class_key s_umount_key;
};
name: the name of the filesystem type, such as "ext2", "iso9660",
next: for internal VFS use: you should initialize this to NULL
+ s_lock_key, s_umount_key: lockdep-specific
+
The get_sb() method has the following arguments:
- struct super_block *sb: the superblock structure. This is partially
- initialized by the VFS and the rest must be initialized by the
- get_sb() method
+ struct file_system_type *fs_type: decribes the filesystem, partly initialized
+ by the specific filesystem code
int flags: mount flags
const char *dev_name: the device name we are mounting.
void *data: arbitrary mount options, usually comes as an ASCII
- string
+ string (see "Mount Options" section)
- int silent: whether or not to be silent on error
+ struct vfsmount *mnt: a vfs-internal representation of a mount point
The get_sb() method must determine if the block device specified
-in the superblock contains a filesystem of the type the method
-supports. On success the method returns the superblock pointer, on
-failure it returns NULL.
+in the dev_name and fs_type contains a filesystem of the type the method
+supports. If it succeeds in opening the named block device, it initializes a
+struct super_block descriptor for the filesystem contained by the block device.
+On failure it returns an error.
The most interesting member of the superblock structure that the
get_sb() method fills in is the "s_op" field. This is a pointer to
must initialize this properly.
void *data: arbitrary mount options, usually comes as an ASCII
- string
+ string (see "Mount Options" section)
int silent: whether or not to be silent on error
-----------------------
This describes how the VFS can manipulate the superblock of your
-filesystem. As of kernel 2.6.13, the following members are defined:
+filesystem. As of kernel 2.6.22, the following members are defined:
struct super_operations {
struct inode *(*alloc_inode)(struct super_block *sb);
void (*destroy_inode)(struct inode *);
- void (*read_inode) (struct inode *);
-
void (*dirty_inode) (struct inode *);
int (*write_inode) (struct inode *, int);
void (*put_inode) (struct inode *);
void (*clear_inode) (struct inode *);
void (*umount_begin) (struct super_block *);
- void (*sync_inodes) (struct super_block *sb,
- struct writeback_control *wbc);
int (*show_options)(struct seq_file *, struct vfsmount *);
ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
->alloc_inode was defined and simply undoes anything done by
->alloc_inode.
- read_inode: this method is called to read a specific inode from the
- mounted filesystem. The i_ino member in the struct inode is
- initialized by the VFS to indicate which inode to read. Other
- members are filled in by this method.
-
- You can set this to NULL and use iget5_locked() instead of iget()
- to read inodes. This is necessary for filesystems for which the
- inode number is not sufficient to identify an inode.
-
dirty_inode: this method is called by the VFS to mark an inode dirty.
write_inode: this method is called when the VFS needs to write an
umount_begin: called when the VFS is unmounting a filesystem.
- sync_inodes: called when the VFS is writing out dirty data associated with
- a superblock.
-
- show_options: called by the VFS to show mount options for /proc/<pid>/mounts.
+ show_options: called by the VFS to show mount options for
+ /proc/<pid>/mounts. (see "Mount Options" section)
quota_read: called by the VFS to read from filesystem quota file.
quota_write: called by the VFS to write to filesystem quota file.
-The read_inode() method is responsible for filling in the "i_op"
-field. This is a pointer to a "struct inode_operations" which
-describes the methods that can be performed on individual inodes.
+Whoever sets up the inode is responsible for filling in the "i_op" field. This
+is a pointer to a "struct inode_operations" which describes the methods that
+can be performed on individual inodes.
The Inode Object
-----------------------
This describes how the VFS can manipulate an inode in your
-filesystem. As of kernel 2.6.13, the following members are defined:
+filesystem. As of kernel 2.6.22, the following members are defined:
struct inode_operations {
int (*create) (struct inode *,struct dentry *,int, struct nameidata *);
ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t);
ssize_t (*listxattr) (struct dentry *, char *, size_t);
int (*removexattr) (struct dentry *, const char *);
+ void (*truncate_range)(struct inode *, loff_t, loff_t);
};
Again, all methods are called without any locks being held, unless
removexattr: called by the VFS to remove an extended attribute from
a file. This method is called by removexattr(2) system call.
+ truncate_range: a method provided by the underlying filesystem to truncate a
+ range of blocks , i.e. punch a hole somewhere in a file.
+
The Address Space Object
========================
-------------------------------
This describes how the VFS can manipulate mapping of a file to page cache in
-your filesystem. As of kernel 2.6.16, the following members are defined:
+your filesystem. As of kernel 2.6.22, the following members are defined:
struct address_space_operations {
int (*writepage)(struct page *page, struct writeback_control *wbc);
struct list_head *pages, unsigned nr_pages);
int (*prepare_write)(struct file *, struct page *, unsigned, unsigned);
int (*commit_write)(struct file *, struct page *, unsigned, unsigned);
+ int (*write_begin)(struct file *, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned flags,
+ struct page **pagep, void **fsdata);
+ int (*write_end)(struct file *, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned copied,
+ struct page *page, void *fsdata);
sector_t (*bmap)(struct address_space *, sector_t);
int (*invalidatepage) (struct page *, unsigned long);
int (*releasepage) (struct page *, int);
int);
/* migrate the contents of a page to the specified target */
int (*migratepage) (struct page *, struct page *);
+ int (*launder_page) (struct page *);
};
writepage: called by the VM to write a dirty page to backing store.
any basic-blocks on storage, then those blocks should be
pre-read (if they haven't been read already) so that the
updated blocks can be written out properly.
- The page will be locked. If prepare_write wants to unlock the
- page it, like readpage, may do so and return
- AOP_TRUNCATED_PAGE.
- In this case the prepare_write will be retried one the lock is
- regained.
+ The page will be locked.
Note: the page _must not_ be marked uptodate in this function
(or anywhere else) unless it actually is uptodate right now. As
operations. It should avoid returning an error if possible -
errors should have been handled by prepare_write.
+ write_begin: This is intended as a replacement for prepare_write. The
+ key differences being that:
+ - it returns a locked page (in *pagep) rather than being
+ given a pre locked page;
+ - it must be able to cope with short writes (where the
+ length passed to write_begin is greater than the number
+ of bytes copied into the page).
+
+ Called by the generic buffered write code to ask the filesystem to
+ prepare to write len bytes at the given offset in the file. The
+ address_space should check that the write will be able to complete,
+ by allocating space if necessary and doing any other internal
+ housekeeping. If the write will update parts of any basic-blocks on
+ storage, then those blocks should be pre-read (if they haven't been
+ read already) so that the updated blocks can be written out properly.
+
+ The filesystem must return the locked pagecache page for the specified
+ offset, in *pagep, for the caller to write into.
+
+ flags is a field for AOP_FLAG_xxx flags, described in
+ include/linux/fs.h.
+
+ A void * may be returned in fsdata, which then gets passed into
+ write_end.
+
+ Returns 0 on success; < 0 on failure (which is the error code), in
+ which case write_end is not called.
+
+ write_end: After a successful write_begin, and data copy, write_end must
+ be called. len is the original len passed to write_begin, and copied
+ is the amount that was able to be copied (copied == len is always true
+ if write_begin was called with the AOP_FLAG_UNINTERRUPTIBLE flag).
+
+ The filesystem must take care of unlocking the page and releasing it
+ refcount, and updating i_size.
+
+ Returns < 0 on failure, otherwise the number of bytes (<= 'copied')
+ that were able to be copied into pagecache.
+
bmap: called by the VFS to map a logical block offset within object to
physical block number. This method is used by the FIBMAP
ioctl and for working with swap-files. To be able to swap to
wants to make it a free page. If ->releasepage succeeds, the
page will be removed from the address_space and become free.
- The second case if when a request has been made to invalidate
+ The second case is when a request has been made to invalidate
some or all pages in an address_space. This can happen
through the fadvice(POSIX_FADV_DONTNEED) system call or by the
filesystem explicitly requesting it as nfs and 9fs do (when
transfer any private data across and update any references
that it has to the page.
+ launder_page: Called before freeing a page - it writes back the dirty page. To
+ prevent redirtying the page, it is kept locked during the whole
+ operation.
+
The File Object
===============
----------------------
This describes how the VFS can manipulate an open file. As of kernel
-2.6.17, the following members are defined:
+2.6.22, the following members are defined:
struct file_operations {
+ struct module *owner;
loff_t (*llseek) (struct file *, loff_t, int);
ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
int (*check_flags)(int);
int (*dir_notify)(struct file *filp, unsigned long arg);
int (*flock) (struct file *, int, struct file_lock *);
- ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, size_t, unsigned
-int);
- ssize_t (*splice_read)(struct file *, struct pipe_inode_info *, size_t, unsigned
-int);
+ ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, size_t, unsigned int);
+ ssize_t (*splice_read)(struct file *, struct pipe_inode_info *, size_t, unsigned int);
};
Again, all methods are called without any locks being held, unless
For further information on dentry locking, please refer to the document
Documentation/filesystems/dentry-locking.txt.
+Mount Options
+=============
+
+Parsing options
+---------------
+
+On mount and remount the filesystem is passed a string containing a
+comma separated list of mount options. The options can have either of
+these forms:
+
+ option
+ option=value
+
+The <linux/parser.h> header defines an API that helps parse these
+options. There are plenty of examples on how to use it in existing
+filesystems.
+
+Showing options
+---------------
+
+If a filesystem accepts mount options, it must define show_options()
+to show all the currently active options. The rules are:
+
+ - options MUST be shown which are not default or their values differ
+ from the default
+
+ - options MAY be shown which are enabled by default or have their
+ default value
+
+Options used only internally between a mount helper and the kernel
+(such as file descriptors), or which only have an effect during the
+mounting (such as ones controlling the creation of a journal) are exempt
+from the above rules.
+
+The underlying reason for the above rules is to make sure, that a
+mount can be accurately replicated (e.g. umounting and mounting again)
+based on the information found in /proc/mounts.
+
+A simple method of saving options at mount/remount time and showing
+them is provided with the save_mount_options() and
+generic_show_options() helper functions. Please note, that using
+these may have drawbacks. For more info see header comments for these
+functions in fs/namespace.c.
Resources
=========
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