diff options
Diffstat (limited to 'Documentation/filesystems/vfs.txt')
| -rw-r--r-- | Documentation/filesystems/vfs.txt | 39 |
1 files changed, 5 insertions, 34 deletions
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index c4d348dabe94..5579bda58a6d 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -492,7 +492,7 @@ written-back to storage typically in whole pages, however the address_space has finer control of write sizes. The read process essentially only requires 'readpage'. The write -process is more complicated and uses prepare_write/commit_write or +process is more complicated and uses write_begin/write_end or set_page_dirty to write data into the address_space, and writepage, sync_page, and writepages to writeback data to storage. @@ -521,8 +521,6 @@ struct address_space_operations { int (*set_page_dirty)(struct page *page); int (*readpages)(struct file *filp, struct address_space *mapping, 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); @@ -598,37 +596,7 @@ struct address_space_operations { readpages is only used for read-ahead, so read errors are ignored. If anything goes wrong, feel free to give up. - prepare_write: called by the generic write path in VM to set up a write - request for a page. This indicates to the address space that - the given range of bytes is about to be written. 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 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 - soon as a page is marked uptodate, it is possible for a concurrent - read(2) to copy it to userspace. - - commit_write: If prepare_write succeeds, new data will be copied - into the page and then commit_write will be called. It will - typically update the size of the file (if appropriate) and - mark the inode as dirty, and do any other related housekeeping - 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). - + write_begin: 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, @@ -640,6 +608,9 @@ struct address_space_operations { The filesystem must return the locked pagecache page for the specified offset, in *pagep, for the caller to write into. + 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). + flags is a field for AOP_FLAG_xxx flags, described in include/linux/fs.h. |