Commit e4ecaf90 authored by Qu Wenruo's avatar Qu Wenruo Committed by David Sterba
Browse files

btrfs: add comments for btrfs_check_can_nocow() and can_nocow_extent() 



These two functions have extra conditions that their callers need to
meet, and some not-that-common parameters used for return value.

So adding some comments may save reviewers some time.

Signed-off-by: default avatarQu Wenruo <wqu@suse.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 6d4572a9

fs/btrfs/file.c

+21 −0
Original line number Diff line number Diff line
@@ -1533,6 +1533,27 @@ lock_and_cleanup_extent_if_need(struct btrfs_inode *inode, struct page **pages, 
	return ret;

}



/*

 * Check if we can do nocow write into the range [@pos, @pos + @write_bytes)

 *

 * @pos:	 File offset

 * @write_bytes: The length to write, will be updated to the nocow writeable

 *		 range

 * @nowait:	 Whether this function could sleep

 *

 * This function will flush ordered extents in the range to ensure proper

 * nocow checks for (nowait == false) case.

 *

 * Return:

 * >0		and update @write_bytes if we can do nocow write

 *  0		if we can't do nocow write

 * -EAGAIN	if we can't get the needed lock or there are ordered extents

 * 		for * (nowait == true) case

 * <0		if other error happened

 *

 * NOTE: For wait (nowait == false) calls, callers need to release the drew

 * write lock of inode->root->snapshot_lock when return value > 0.

 */

int btrfs_check_can_nocow(struct btrfs_inode *inode, loff_t pos,

			  size_t *write_bytes, bool nowait)

{

fs/btrfs/inode.c

+19 −2
Original line number Diff line number Diff line
@@ -6945,8 +6945,25 @@ static struct extent_map *btrfs_new_extent_direct(struct inode *inode, 
}



/*

 * returns 1 when the nocow is safe, < 1 on error, 0 if the

 * block must be cow'd

 * Check if we can do nocow write into the range [@offset, @offset + @len)

 *

 * @offset:	File offset

 * @len:	The length to write, will be updated to the nocow writeable

 *		range

 * @orig_start:	(optional) Return the original file offset of the file extent

 * @orig_len:	(optional) Return the original on-disk length of the file extent

 * @ram_bytes:	(optional) Return the ram_bytes of the file extent

 *

 * This function will flush ordered extents in the range to ensure proper

 * nocow checks for (nowait == false) case.

 *

 * Return:

 * >0	and update @len if we can do nocow write

 *  0	if we can't do nocow write

 * <0	if error happened

 *

 * NOTE: This only checks the file extents, caller is responsible to wait for

 *	 any ordered extents.

 */

noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,

			      u64 *orig_start, u64 *orig_block_len,