From: Darrick J. Wong <djwong@xxxxxxxxxx>
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@xxxxxxxxxx>
---
fs/xfs/xfs_fsmap.c | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)
diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c
index 7d0b09c1366e..a0e8ab58124b 100644
--- a/fs/xfs/xfs_fsmap.c
+++ b/fs/xfs/xfs_fsmap.c
@@ -523,27 +523,39 @@ 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 extents covering the range we
+ * want.
+ */
alow.ar_startext = info->low.rm_startblock;
+ do_div(alow.ar_startext, mp->m_sb.sb_rextsize);
+
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))
+ 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;
}
