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xfs: fix off-by-one error when the last rt extent is in use

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The fsmap implementation for realtime devices uses the gap between
info->next_daddr and a free rtextent reported by xfs_rtalloc_query_range
to feed userspace fsmap records with an "unknown" owner.  We use this
trick to report to userspace when the last rtextent in the filesystem is
in use by synthesizing a null rmap record starting at the next block
after the query range.

Unfortunately, there's a minor accounting bug in the way that we
construct the null rmap record.  Originally, ahigh.ar_startext contains
the last rtextent for which the user wants records.  It's entirely
possible that number is beyond the end of the rt volume, so the location
synthesized rmap record /must/ be constrained to the minimum of the high
key and the number of extents in the rt volume.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
This commit is contained in:
Darrick J. Wong 2021-08-10 17:00:31 -07:00
parent c02f652986
commit 9ab72f2227
1 changed files with 15 additions and 5 deletions
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20
fs/xfs/xfs_fsmap.c
View file

@ -523,27 +523,37 @@ xfs_getfsmap_rtdev_rtbitmap_query(
{
struct xfs_rtalloc_rec alow = { 0 };
struct xfs_rtalloc_rec ahigh = { 0 };
struct xfs_mount *mp = tp->t_mountp;
int error;
xfs_ilock(tp->t_mountp->m_rbmip, XFS_ILOCK_SHARED);
xfs_ilock(mp->m_rbmip, XFS_ILOCK_SHARED);
/*
* Set up query parameters to return free rtextents covering the range
* we want.
*/
alow.ar_startext = info->low.rm_startblock;
ahigh.ar_startext = info->high.rm_startblock;
do_div(alow.ar_startext, tp->t_mountp->m_sb.sb_rextsize);
if (do_div(ahigh.ar_startext, tp->t_mountp->m_sb.sb_rextsize))
do_div(alow.ar_startext, mp->m_sb.sb_rextsize);
if (do_div(ahigh.ar_startext, mp->m_sb.sb_rextsize))
ahigh.ar_startext++;
error = xfs_rtalloc_query_range(tp, &alow, &ahigh,
xfs_getfsmap_rtdev_rtbitmap_helper, info);
if (error)
goto err;
/* Report any gaps at the end of the rtbitmap */
/*
* Report any gaps at the end of the rtbitmap by simulating a null
* rmap starting at the block after the end of the query range.
*/
info->last = true;
ahigh.ar_startext = min(mp->m_sb.sb_rextents, ahigh.ar_startext);
error = xfs_getfsmap_rtdev_rtbitmap_helper(tp, &ahigh, info);
if (error)
goto err;
err:
xfs_iunlock(tp->t_mountp->m_rbmip, XFS_ILOCK_SHARED);
xfs_iunlock(mp->m_rbmip, XFS_ILOCK_SHARED);
return error;
}