[PATCH v2 5/9] xfs: bmap scrubber should do rmap xref with bmap for sparse files

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

When we're scanning an extent mapping inode fork, ensure that every rmap
record for this ifork has a corresponding bmbt record too.  This
(mostly) provides the ability to cross-reference rmap records with bmap
data.  The rmap scrubber cannot do the xref on its own because that
requires taking an ilock with the agf lock held, which violates our
locking order rules (inode, then agf).

Note that we only do this for forks that are in btree format due to the
increased complexity; or forks that should have data but suspiciously
have zero extents because the inode could have just had its iforks
zapped by the inode repair code and now we need to reclaim the old
extents.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
v2: enhance comments, fix XFS_BTREE_ERROR usage
---
 fs/xfs/scrub/bmap.c |  170 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 169 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/scrub/bmap.c b/fs/xfs/scrub/bmap.c
index d002821..75ea2d6 100644
--- a/fs/xfs/scrub/bmap.c
+++ b/fs/xfs/scrub/bmap.c
@@ -37,6 +37,7 @@
 #include "xfs_bmap_util.h"
 #include "xfs_bmap_btree.h"
 #include "xfs_rmap.h"
+#include "xfs_rmap_btree.h"
 #include "xfs_refcount.h"
 #include "scrub/xfs_scrub.h"
 #include "scrub/scrub.h"
@@ -423,6 +424,169 @@ xfs_scrub_bmap_btree(
 	return error;
 }
 
+struct xfs_scrub_bmap_check_rmap_info {
+	struct xfs_scrub_context	*sc;
+	int				whichfork;
+	struct xfs_iext_cursor		icur;
+};
+
+/* Can we find bmaps that fit this rmap? */
+STATIC int
+xfs_scrub_bmap_check_rmap(
+	struct xfs_btree_cur		*cur,
+	struct xfs_rmap_irec		*rec,
+	void				*priv)
+{
+	struct xfs_bmbt_irec		irec;
+	struct xfs_scrub_bmap_check_rmap_info	*sbcri = priv;
+	struct xfs_ifork		*ifp;
+	struct xfs_scrub_context	*sc = sbcri->sc;
+	bool				have_map;
+
+	/* Is this even the right fork? */
+	if (rec->rm_owner != sc->ip->i_ino)
+		return 0;
+	if ((sbcri->whichfork == XFS_ATTR_FORK) ^
+	    !!(rec->rm_flags & XFS_RMAP_ATTR_FORK))
+		return 0;
+	if (rec->rm_flags & XFS_RMAP_BMBT_BLOCK)
+		return 0;
+
+	/* Now look up the bmbt record. */
+	ifp = XFS_IFORK_PTR(sc->ip, sbcri->whichfork);
+	if (!ifp) {
+		xfs_scrub_fblock_set_corrupt(sc, sbcri->whichfork,
+				rec->rm_offset);
+		goto out;
+	}
+	have_map = xfs_iext_lookup_extent(sc->ip, ifp, rec->rm_offset,
+			&sbcri->icur, &irec);
+	if (!have_map)
+		xfs_scrub_fblock_set_corrupt(sc, sbcri->whichfork,
+				rec->rm_offset);
+	/*
+	 * bmap extent record lengths are constrained to 2^21 blocks in length
+	 * because of space constraints in the on-disk metadata structure.
+	 * However, rmap extent record lengths are constrained only by AG
+	 * length, so we have to loop through the bmbt to make sure that the
+	 * entire rmap is covered by bmbt records.
+	 */
+	while (have_map) {
+		if (irec.br_startoff != rec->rm_offset)
+			xfs_scrub_fblock_set_corrupt(sc, sbcri->whichfork,
+					rec->rm_offset);
+		if (irec.br_startblock != XFS_AGB_TO_FSB(sc->mp,
+				cur->bc_private.a.agno, rec->rm_startblock))
+			xfs_scrub_fblock_set_corrupt(sc, sbcri->whichfork,
+					rec->rm_offset);
+		if (irec.br_blockcount > rec->rm_blockcount)
+			xfs_scrub_fblock_set_corrupt(sc, sbcri->whichfork,
+					rec->rm_offset);
+		if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
+			break;
+		rec->rm_startblock += irec.br_blockcount;
+		rec->rm_offset += irec.br_blockcount;
+		rec->rm_blockcount -= irec.br_blockcount;
+		if (rec->rm_blockcount == 0)
+			break;
+		have_map = xfs_iext_next_extent(ifp, &sbcri->icur, &irec);
+		if (!have_map)
+			xfs_scrub_fblock_set_corrupt(sc, sbcri->whichfork,
+					rec->rm_offset);
+	}
+
+out:
+	if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
+		return XFS_BTREE_QUERY_RANGE_ABORT;
+	return 0;
+}
+
+/* Make sure each rmap has a corresponding bmbt entry. */
+STATIC int
+xfs_scrub_bmap_check_ag_rmaps(
+	struct xfs_scrub_context	*sc,
+	int				whichfork,
+	xfs_agnumber_t			agno)
+{
+	struct xfs_scrub_bmap_check_rmap_info	sbcri;
+	struct xfs_btree_cur		*cur;
+	struct xfs_buf			*agf;
+	int				error;
+
+	error = xfs_alloc_read_agf(sc->mp, sc->tp, agno, 0, &agf);
+	if (error)
+		return error;
+
+	cur = xfs_rmapbt_init_cursor(sc->mp, sc->tp, agf, agno);
+	if (!cur) {
+		error = -ENOMEM;
+		goto out_agf;
+	}
+
+	sbcri.sc = sc;
+	sbcri.whichfork = whichfork;
+	error = xfs_rmap_query_all(cur, xfs_scrub_bmap_check_rmap, &sbcri);
+	if (error == XFS_BTREE_QUERY_RANGE_ABORT)
+		error = 0;
+
+	xfs_btree_del_cursor(cur, error ? XFS_BTREE_ERROR : XFS_BTREE_NOERROR);
+out_agf:
+	xfs_trans_brelse(sc->tp, agf);
+	return error;
+}
+
+/* Make sure each rmap has a corresponding bmbt entry. */
+STATIC int
+xfs_scrub_bmap_check_rmaps(
+	struct xfs_scrub_context	*sc,
+	int				whichfork)
+{
+	loff_t				size;
+	xfs_agnumber_t			agno;
+	int				error;
+
+	if (!xfs_sb_version_hasrmapbt(&sc->mp->m_sb) ||
+	    whichfork == XFS_COW_FORK ||
+	    (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT))
+		return 0;
+
+	/* Don't support realtime rmap checks yet. */
+	if (XFS_IS_REALTIME_INODE(sc->ip) && whichfork == XFS_DATA_FORK)
+		return 0;
+
+	/*
+	 * Only do this for complex maps that are in btree format, or for
+	 * situations where we would seem to have a size but zero extents.
+	 * The inode repair code can zap broken iforks, which means we have
+	 * to flag this bmap as corrupt if there are rmaps that need to be
+	 * reattached.
+	 */
+	switch (whichfork) {
+	case XFS_DATA_FORK:
+		size = i_size_read(VFS_I(sc->ip));
+		break;
+	case XFS_ATTR_FORK:
+		size = XFS_IFORK_Q(sc->ip);
+		break;
+	default:
+		size = 0;
+		break;
+	}
+	if (XFS_IFORK_FORMAT(sc->ip, whichfork) != XFS_DINODE_FMT_BTREE &&
+	    (size == 0 || XFS_IFORK_NEXTENTS(sc->ip, whichfork) > 0))
+		return 0;
+
+	for (agno = 0; agno < sc->mp->m_sb.sb_agcount; agno++) {
+		error = xfs_scrub_bmap_check_ag_rmaps(sc, whichfork, agno);
+		if (error)
+			return error;
+		if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
+			break;
+	}
+
+	return 0;
+}
+
 /*
  * Scrub an inode fork's block mappings.
  *
@@ -463,7 +627,7 @@ xfs_scrub_bmap(
 		break;
 	case XFS_ATTR_FORK:
 		if (!ifp)
-			goto out;
+			goto out_check_rmap;
 		if (!xfs_sb_version_hasattr(&mp->m_sb) &&
 		    !xfs_sb_version_hasattr2(&mp->m_sb))
 			xfs_scrub_ino_set_corrupt(sc, sc->ip->i_ino, NULL);
@@ -534,6 +698,10 @@ xfs_scrub_bmap(
 			goto out;
 	}
 
+out_check_rmap:
+	error = xfs_scrub_bmap_check_rmaps(sc, whichfork);
+	if (!xfs_scrub_fblock_xref_process_error(sc, whichfork, 0, &error))
+		goto out;
 out:
 	return error;
 }