[PATCH] Don't do I/O beyond eof when unreserving space

[PATCH] Don't do I/O beyond eof when unreserving space

[Lachlan McIlroy]

When unreserving space with boundaries that are not block aligned we round
up the start and round down the end boundaries and then use this function,
xfs_zero_remaining_bytes(), to zero the parts of the blocks that got dropped
during the rounding.  The problem is we don't consider if these blocks are
beyond eof.  Worse still is if we encounter delayed allocations beyond eof
we will try to use the magic delayed allocation block number as a real block
number.  If the file size is ever extended to expose these blocks then we'll
go through xfs_zero_eof() to zero them anyway.

--- a/fs/xfs/xfs_vnodeops.c	2008-09-02 14:54:24.000000000 +1000
+++ b/fs/xfs/xfs_vnodeops.c	2008-09-02 14:51:03.000000000 +1000
@@ -3176,6 +3176,12 @@ xfs_zero_remaining_bytes(
 	int			nimap;
 	int			error = 0;
 
+	if (startoff >= ip->i_size)
+		return 0;
+
+	if (endoff > ip->i_size)
+		endoff = ip->i_size;
+
 	bp = xfs_buf_get_noaddr(mp->m_sb.sb_blocksize,
 				XFS_IS_REALTIME_INODE(ip) ?
 				mp->m_rtdev_targp : mp->m_ddev_targp);

Re: [PATCH] Don't do I/O beyond eof when unreserving space

[Christoph Hellwig]

On Tue, Sep 02, 2008 at 03:24:57PM +1000, Lachlan McIlroy wrote:
> When unreserving space with boundaries that are not block aligned we round
> up the start and round down the end boundaries and then use this function,
> xfs_zero_remaining_bytes(), to zero the parts of the blocks that got dropped
> during the rounding.  The problem is we don't consider if these blocks are
> beyond eof.  Worse still is if we encounter delayed allocations beyond eof
> we will try to use the magic delayed allocation block number as a real block
> number.  If the file size is ever extended to expose these blocks then we'll
> go through xfs_zero_eof() to zero them anyway.

Makes sense.  Would be nice to have a comment above the check explaining
why these first strange checks are there.  Something like the first
setence of the patch description here.