Commit 9ab72f22 authored by Darrick J. Wong's avatar Darrick J. Wong
Browse files

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



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: default avatarDarrick J. Wong <djwong@kernel.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarChandan Babu R <chandanrlinux@gmail.com>
parent c02f6529

fs/xfs/xfs_fsmap.c

+15 −5
Original line number Diff line number Diff line
@@ -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;

}