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authorNick Piggin <npiggin@suse.de>2007-10-16 04:25:01 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-16 12:42:55 -0400
commitafddba49d18f346e5cc2938b6ed7c512db18ca68 (patch)
tree4726e3d3b0e9e8e5b5d3b2b0cccb36446bbdf3ca /Documentation/filesystems/vfs.txt
parent637aff46f94a754207c80c8c64bf1b74f24b967d (diff)
fs: introduce write_begin, write_end, and perform_write aops
These are intended to replace prepare_write and commit_write with more flexible alternatives that are also able to avoid the buffered write deadlock problems efficiently (which prepare_write is unable to do). [mark.fasheh@oracle.com: API design contributions, code review and fixes] [akpm@linux-foundation.org: various fixes] [dmonakhov@sw.ru: new aop block_write_begin fix] Signed-off-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com> Signed-off-by: Dmitriy Monakhov <dmonakhov@openvz.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/filesystems/vfs.txt')
-rw-r--r--Documentation/filesystems/vfs.txt45
1 files changed, 45 insertions, 0 deletions
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 045f3e055a28..281c19ff7f45 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -537,6 +537,12 @@ struct address_space_operations {
537 struct list_head *pages, unsigned nr_pages); 537 struct list_head *pages, unsigned nr_pages);
538 int (*prepare_write)(struct file *, struct page *, unsigned, unsigned); 538 int (*prepare_write)(struct file *, struct page *, unsigned, unsigned);
539 int (*commit_write)(struct file *, struct page *, unsigned, unsigned); 539 int (*commit_write)(struct file *, struct page *, unsigned, unsigned);
540 int (*write_begin)(struct file *, struct address_space *mapping,
541 loff_t pos, unsigned len, unsigned flags,
542 struct page **pagep, void **fsdata);
543 int (*write_end)(struct file *, struct address_space *mapping,
544 loff_t pos, unsigned len, unsigned copied,
545 struct page *page, void *fsdata);
540 sector_t (*bmap)(struct address_space *, sector_t); 546 sector_t (*bmap)(struct address_space *, sector_t);
541 int (*invalidatepage) (struct page *, unsigned long); 547 int (*invalidatepage) (struct page *, unsigned long);
542 int (*releasepage) (struct page *, int); 548 int (*releasepage) (struct page *, int);
@@ -633,6 +639,45 @@ struct address_space_operations {
633 operations. It should avoid returning an error if possible - 639 operations. It should avoid returning an error if possible -
634 errors should have been handled by prepare_write. 640 errors should have been handled by prepare_write.
635 641
642 write_begin: This is intended as a replacement for prepare_write. The
643 key differences being that:
644 - it returns a locked page (in *pagep) rather than being
645 given a pre locked page;
646 - it must be able to cope with short writes (where the
647 length passed to write_begin is greater than the number
648 of bytes copied into the page).
649
650 Called by the generic buffered write code to ask the filesystem to
651 prepare to write len bytes at the given offset in the file. The
652 address_space should check that the write will be able to complete,
653 by allocating space if necessary and doing any other internal
654 housekeeping. If the write will update parts of any basic-blocks on
655 storage, then those blocks should be pre-read (if they haven't been
656 read already) so that the updated blocks can be written out properly.
657
658 The filesystem must return the locked pagecache page for the specified
659 offset, in *pagep, for the caller to write into.
660
661 flags is a field for AOP_FLAG_xxx flags, described in
662 include/linux/fs.h.
663
664 A void * may be returned in fsdata, which then gets passed into
665 write_end.
666
667 Returns 0 on success; < 0 on failure (which is the error code), in
668 which case write_end is not called.
669
670 write_end: After a successful write_begin, and data copy, write_end must
671 be called. len is the original len passed to write_begin, and copied
672 is the amount that was able to be copied (copied == len is always true
673 if write_begin was called with the AOP_FLAG_UNINTERRUPTIBLE flag).
674
675 The filesystem must take care of unlocking the page and releasing it
676 refcount, and updating i_size.
677
678 Returns < 0 on failure, otherwise the number of bytes (<= 'copied')
679 that were able to be copied into pagecache.
680
636 bmap: called by the VFS to map a logical block offset within object to 681 bmap: called by the VFS to map a logical block offset within object to
637 physical block number. This method is used by the FIBMAP 682 physical block number. This method is used by the FIBMAP
638 ioctl and for working with swap-files. To be able to swap to 683 ioctl and for working with swap-files. To be able to swap to