2 * "splice": joining two ropes together by interweaving their strands.
4 * This is the "extended pipe" functionality, where a pipe is used as
5 * an arbitrary in-memory buffer. Think of a pipe as a small kernel
6 * buffer that you can use to transfer data from one end to the other.
8 * The traditional unix read/write is extended with a "splice()" operation
9 * that transfers data buffers to or from a pipe buffer.
11 * Named by Larry McVoy, original implementation from Linus, extended by
12 * Jens to support splicing to files and fixing the initial implementation
15 * Copyright (C) 2005 Jens Axboe <axboe@suse.de>
16 * Copyright (C) 2005 Linus Torvalds <torvalds@osdl.org>
20 #include <linux/file.h>
21 #include <linux/pagemap.h>
22 #include <linux/pipe_fs_i.h>
23 #include <linux/mm_inline.h>
24 #include <linux/swap.h>
25 #include <linux/writeback.h>
26 #include <linux/buffer_head.h>
27 #include <linux/module.h>
28 #include <linux/syscalls.h>
31 * Passed to the actors
34 unsigned int len, total_len; /* current and remaining length */
35 unsigned int flags; /* splice flags */
36 struct file *file; /* file to read/write */
37 loff_t pos; /* file position */
41 * Attempt to steal a page from a pipe buffer. This should perhaps go into
42 * a vm helper function, it's already simplified quite a bit by the
43 * addition of remove_mapping(). If success is returned, the caller may
44 * attempt to reuse this page for another destination.
46 static int page_cache_pipe_buf_steal(struct pipe_inode_info *info,
47 struct pipe_buffer *buf)
49 struct page *page = buf->page;
50 struct address_space *mapping = page_mapping(page);
52 WARN_ON(!PageLocked(page));
53 WARN_ON(!PageUptodate(page));
56 * At least for ext2 with nobh option, we need to wait on writeback
57 * completing on this page, since we'll remove it from the pagecache.
58 * Otherwise truncate wont wait on the page, allowing the disk
59 * blocks to be reused by someone else before we actually wrote our
60 * data to them. fs corruption ensues.
62 wait_on_page_writeback(page);
64 if (PagePrivate(page))
65 try_to_release_page(page, mapping_gfp_mask(mapping));
67 if (!remove_mapping(mapping, page))
70 buf->flags |= PIPE_BUF_FLAG_STOLEN | PIPE_BUF_FLAG_LRU;
74 static void page_cache_pipe_buf_release(struct pipe_inode_info *info,
75 struct pipe_buffer *buf)
77 page_cache_release(buf->page);
79 buf->flags &= ~(PIPE_BUF_FLAG_STOLEN | PIPE_BUF_FLAG_LRU);
82 static void *page_cache_pipe_buf_map(struct file *file,
83 struct pipe_inode_info *info,
84 struct pipe_buffer *buf)
86 struct page *page = buf->page;
89 if (!PageUptodate(page)) {
93 * Page got truncated/unhashed. This will cause a 0-byte
94 * splice, if this is the first page
102 * uh oh, read-error from disk
104 if (!PageUptodate(page)) {
110 * page is ok afterall, fall through to mapping
121 static void page_cache_pipe_buf_unmap(struct pipe_inode_info *info,
122 struct pipe_buffer *buf)
127 static struct pipe_buf_operations page_cache_pipe_buf_ops = {
129 .map = page_cache_pipe_buf_map,
130 .unmap = page_cache_pipe_buf_unmap,
131 .release = page_cache_pipe_buf_release,
132 .steal = page_cache_pipe_buf_steal,
136 * Pipe output worker. This sets up our pipe format with the page cache
137 * pipe buffer operations. Otherwise very similar to the regular pipe_writev().
139 static ssize_t move_to_pipe(struct pipe_inode_info *pipe, struct page **pages,
140 int nr_pages, unsigned long offset,
141 unsigned long len, unsigned int flags)
143 int ret, do_wakeup, i;
150 mutex_lock(&pipe->inode->i_mutex);
155 if (!pipe->readers) {
156 send_sig(SIGPIPE, current, 0);
163 if (bufs < PIPE_BUFFERS) {
164 int newbuf = (pipe->curbuf + bufs) & (PIPE_BUFFERS - 1);
165 struct pipe_buffer *buf = pipe->bufs + newbuf;
166 struct page *page = pages[i++];
167 unsigned long this_len;
169 this_len = PAGE_CACHE_SIZE - offset;
174 buf->offset = offset;
176 buf->ops = &page_cache_pipe_buf_ops;
177 pipe->nrbufs = ++bufs;
187 if (bufs < PIPE_BUFFERS)
193 if (flags & SPLICE_F_NONBLOCK) {
199 if (signal_pending(current)) {
207 if (waitqueue_active(&pipe->wait))
208 wake_up_interruptible_sync(&pipe->wait);
209 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
213 pipe->waiting_writers++;
215 pipe->waiting_writers--;
219 mutex_unlock(&pipe->inode->i_mutex);
223 if (waitqueue_active(&pipe->wait))
224 wake_up_interruptible(&pipe->wait);
225 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
229 page_cache_release(pages[i++]);
235 __generic_file_splice_read(struct file *in, struct pipe_inode_info *pipe,
236 size_t len, unsigned int flags)
238 struct address_space *mapping = in->f_mapping;
239 unsigned int offset, nr_pages;
240 struct page *pages[PIPE_BUFFERS];
245 index = in->f_pos >> PAGE_CACHE_SHIFT;
246 offset = in->f_pos & ~PAGE_CACHE_MASK;
247 nr_pages = (len + offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
249 if (nr_pages > PIPE_BUFFERS)
250 nr_pages = PIPE_BUFFERS;
253 * initiate read-ahead on this page range. however, don't call into
254 * read-ahead if this is a non-zero offset (we are likely doing small
255 * chunk splice and the page is already there) for a single page.
257 if (!offset || nr_pages > 1)
258 do_page_cache_readahead(mapping, in, index, nr_pages);
261 * now fill in the holes
263 for (i = 0; i < nr_pages; i++, index++) {
265 * no page there, look one up / create it
267 page = find_or_create_page(mapping, index,
268 mapping_gfp_mask(mapping));
272 if (PageUptodate(page))
275 int error = mapping->a_ops->readpage(in, page);
277 if (unlikely(error)) {
278 page_cache_release(page);
286 return move_to_pipe(pipe, pages, i, offset, len, flags);
292 * generic_file_splice_read - splice data from file to a pipe
293 * @in: file to splice from
294 * @pipe: pipe to splice to
295 * @len: number of bytes to splice
296 * @flags: splice modifier flags
298 * Will read pages from given file and fill them into a pipe.
301 ssize_t generic_file_splice_read(struct file *in, struct pipe_inode_info *pipe,
302 size_t len, unsigned int flags)
311 ret = __generic_file_splice_read(in, pipe, len, flags);
320 if (!(flags & SPLICE_F_NONBLOCK))
332 EXPORT_SYMBOL(generic_file_splice_read);
335 * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
338 static int pipe_to_sendpage(struct pipe_inode_info *info,
339 struct pipe_buffer *buf, struct splice_desc *sd)
341 struct file *file = sd->file;
342 loff_t pos = sd->pos;
349 * sub-optimal, but we are limited by the pipe ->map. we don't
350 * need a kmap'ed buffer here, we just want to make sure we
351 * have the page pinned if the pipe page originates from the
354 ptr = buf->ops->map(file, info, buf);
358 offset = pos & ~PAGE_CACHE_MASK;
359 more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
361 ret = file->f_op->sendpage(file, buf->page, offset, sd->len, &pos,more);
363 buf->ops->unmap(info, buf);
371 * This is a little more tricky than the file -> pipe splicing. There are
372 * basically three cases:
374 * - Destination page already exists in the address space and there
375 * are users of it. For that case we have no other option that
376 * copying the data. Tough luck.
377 * - Destination page already exists in the address space, but there
378 * are no users of it. Make sure it's uptodate, then drop it. Fall
379 * through to last case.
380 * - Destination page does not exist, we can add the pipe page to
381 * the page cache and avoid the copy.
383 * If asked to move pages to the output file (SPLICE_F_MOVE is set in
384 * sd->flags), we attempt to migrate pages from the pipe to the output
385 * file address space page cache. This is possible if no one else has
386 * the pipe page referenced outside of the pipe and page cache. If
387 * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
388 * a new page in the output file page cache and fill/dirty that.
390 static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
391 struct splice_desc *sd)
393 struct file *file = sd->file;
394 struct address_space *mapping = file->f_mapping;
395 gfp_t gfp_mask = mapping_gfp_mask(mapping);
403 * make sure the data in this buffer is uptodate
405 src = buf->ops->map(file, info, buf);
409 index = sd->pos >> PAGE_CACHE_SHIFT;
410 offset = sd->pos & ~PAGE_CACHE_MASK;
413 * reuse buf page, if SPLICE_F_MOVE is set
415 if (sd->flags & SPLICE_F_MOVE) {
417 * If steal succeeds, buf->page is now pruned from the vm
418 * side (LRU and page cache) and we can reuse it.
420 if (buf->ops->steal(info, buf))
424 * this will also set the page locked
427 if (add_to_page_cache(page, mapping, index, gfp_mask))
430 if (!(buf->flags & PIPE_BUF_FLAG_LRU))
435 page = find_or_create_page(mapping, index, gfp_mask);
440 * If the page is uptodate, it is also locked. If it isn't
441 * uptodate, we can mark it uptodate if we are filling the
442 * full page. Otherwise we need to read it in first...
444 if (!PageUptodate(page)) {
445 if (sd->len < PAGE_CACHE_SIZE) {
446 ret = mapping->a_ops->readpage(file, page);
452 if (!PageUptodate(page)) {
454 * page got invalidated, repeat
456 if (!page->mapping) {
458 page_cache_release(page);
465 WARN_ON(!PageLocked(page));
466 SetPageUptodate(page);
471 ret = mapping->a_ops->prepare_write(file, page, 0, sd->len);
472 if (ret == AOP_TRUNCATED_PAGE) {
473 page_cache_release(page);
478 if (!(buf->flags & PIPE_BUF_FLAG_STOLEN)) {
479 char *dst = kmap_atomic(page, KM_USER0);
481 memcpy(dst + offset, src + buf->offset, sd->len);
482 flush_dcache_page(page);
483 kunmap_atomic(dst, KM_USER0);
486 ret = mapping->a_ops->commit_write(file, page, 0, sd->len);
487 if (ret == AOP_TRUNCATED_PAGE) {
488 page_cache_release(page);
493 mark_page_accessed(page);
494 balance_dirty_pages_ratelimited(mapping);
496 if (!(buf->flags & PIPE_BUF_FLAG_STOLEN)) {
497 page_cache_release(page);
501 buf->ops->unmap(info, buf);
505 typedef int (splice_actor)(struct pipe_inode_info *, struct pipe_buffer *,
506 struct splice_desc *);
509 * Pipe input worker. Most of this logic works like a regular pipe, the
510 * key here is the 'actor' worker passed in that actually moves the data
511 * to the wanted destination. See pipe_to_file/pipe_to_sendpage above.
513 static ssize_t move_from_pipe(struct pipe_inode_info *pipe, struct file *out,
514 size_t len, unsigned int flags,
517 int ret, do_wakeup, err;
518 struct splice_desc sd;
529 mutex_lock(&pipe->inode->i_mutex);
532 int bufs = pipe->nrbufs;
535 int curbuf = pipe->curbuf;
536 struct pipe_buffer *buf = pipe->bufs + curbuf;
537 struct pipe_buf_operations *ops = buf->ops;
540 if (sd.len > sd.total_len)
541 sd.len = sd.total_len;
543 err = actor(pipe, buf, &sd);
545 if (!ret && err != -ENODATA)
552 buf->offset += sd.len;
556 ops->release(pipe, buf);
557 curbuf = (curbuf + 1) & (PIPE_BUFFERS - 1);
558 pipe->curbuf = curbuf;
559 pipe->nrbufs = --bufs;
564 sd.total_len -= sd.len;
573 if (!pipe->waiting_writers) {
578 if (flags & SPLICE_F_NONBLOCK) {
584 if (signal_pending(current)) {
592 if (waitqueue_active(&pipe->wait))
593 wake_up_interruptible_sync(&pipe->wait);
594 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
602 mutex_unlock(&pipe->inode->i_mutex);
606 if (waitqueue_active(&pipe->wait))
607 wake_up_interruptible(&pipe->wait);
608 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
611 mutex_lock(&out->f_mapping->host->i_mutex);
613 mutex_unlock(&out->f_mapping->host->i_mutex);
619 * generic_file_splice_write - splice data from a pipe to a file
621 * @out: file to write to
622 * @len: number of bytes to splice
623 * @flags: splice modifier flags
625 * Will either move or copy pages (determined by @flags options) from
626 * the given pipe inode to the given file.
630 generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
631 size_t len, unsigned int flags)
633 struct address_space *mapping = out->f_mapping;
636 ret = move_from_pipe(pipe, out, len, flags, pipe_to_file);
639 * if file or inode is SYNC and we actually wrote some data, sync it
641 if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(mapping->host))
643 struct inode *inode = mapping->host;
646 mutex_lock(&inode->i_mutex);
647 err = generic_osync_inode(mapping->host, mapping,
648 OSYNC_METADATA|OSYNC_DATA);
649 mutex_unlock(&inode->i_mutex);
658 EXPORT_SYMBOL(generic_file_splice_write);
661 * generic_splice_sendpage - splice data from a pipe to a socket
663 * @out: socket to write to
664 * @len: number of bytes to splice
665 * @flags: splice modifier flags
667 * Will send @len bytes from the pipe to a network socket. No data copying
671 ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
672 size_t len, unsigned int flags)
674 return move_from_pipe(pipe, out, len, flags, pipe_to_sendpage);
677 EXPORT_SYMBOL(generic_splice_sendpage);
680 * Attempt to initiate a splice from pipe to file.
682 static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
683 loff_t __user *off_out, size_t len,
689 if (!out->f_op || !out->f_op->splice_write)
692 if (!(out->f_mode & FMODE_WRITE))
695 if (off_out && copy_from_user(&out->f_pos, off_out, sizeof(loff_t)))
700 ret = rw_verify_area(WRITE, out, &pos, len);
701 if (unlikely(ret < 0))
704 return out->f_op->splice_write(pipe, out, len, flags);
708 * Attempt to initiate a splice from a file to a pipe.
710 static long do_splice_to(struct file *in, loff_t __user *off_in,
711 struct pipe_inode_info *pipe, size_t len,
714 loff_t pos, isize, left;
717 if (!in->f_op || !in->f_op->splice_read)
720 if (!(in->f_mode & FMODE_READ))
723 if (off_in && copy_from_user(&in->f_pos, off_in, sizeof(loff_t)))
728 ret = rw_verify_area(READ, in, &pos, len);
729 if (unlikely(ret < 0))
732 isize = i_size_read(in->f_mapping->host);
733 if (unlikely(in->f_pos >= isize))
736 left = isize - in->f_pos;
740 return in->f_op->splice_read(in, pipe, len, flags);
744 * Determine where to splice to/from.
746 static long do_splice(struct file *in, loff_t __user *off_in,
747 struct file *out, loff_t __user *off_out,
748 size_t len, unsigned int flags)
750 struct pipe_inode_info *pipe;
752 if (off_out && out->f_op->llseek == no_llseek)
754 if (off_in && in->f_op->llseek == no_llseek)
757 pipe = in->f_dentry->d_inode->i_pipe;
762 return do_splice_from(pipe, out, off_out, len, flags);
765 pipe = out->f_dentry->d_inode->i_pipe;
770 return do_splice_to(in, off_in, pipe, len, flags);
776 asmlinkage long sys_splice(int fd_in, loff_t __user *off_in,
777 int fd_out, loff_t __user *off_out,
778 size_t len, unsigned int flags)
781 struct file *in, *out;
782 int fput_in, fput_out;
788 in = fget_light(fd_in, &fput_in);
790 if (in->f_mode & FMODE_READ) {
791 out = fget_light(fd_out, &fput_out);
793 if (out->f_mode & FMODE_WRITE)
794 error = do_splice(in, off_in,
797 fput_light(out, fput_out);
801 fput_light(in, fput_in);