xfs: teach scrub to check for adjacent bmaps when rmap larger than bmap

When scrub is checking file fork mappings against rmap records and
the rmap record starts before or ends after the bmap record, check the
adjacent bmap records to make sure that they're adjacent to the one
we're checking.  This helps us to detect cases where the rmaps cover
territory that the bmaps do not.
Signed-off-by: NDarrick J. Wong <djwong@kernel.org>
Reviewed-by: NDave Chinner <dchinner@redhat.com>

fs/xfs/scrub/bmap.c

@@ -90,6 +90,7 @@ xchk_setup_inode_bmap(
 
 struct xchk_bmap_info {
 	struct xfs_scrub	*sc;
+	struct xfs_iext_cursor	icur;
 	xfs_fileoff_t		lastoff;
 	bool			is_rt;
 	bool			is_shared;
@@ -146,6 +147,48 @@ xchk_bmap_get_rmap(
 	return has_rmap;
 }
 
+static inline bool
+xchk_bmap_has_prev(
+	struct xchk_bmap_info	*info,
+	struct xfs_bmbt_irec	*irec)
+{
+	struct xfs_bmbt_irec	got;
+	struct xfs_ifork	*ifp;
+
+	ifp = xfs_ifork_ptr(info->sc->ip, info->whichfork);
+
+	if (!xfs_iext_peek_prev_extent(ifp, &info->icur, &got))
+		return false;
+	if (got.br_startoff + got.br_blockcount != irec->br_startoff)
+		return false;
+	if (got.br_startblock + got.br_blockcount != irec->br_startblock)
+		return false;
+	if (got.br_state != irec->br_state)
+		return false;
+	return true;
+}
+
+static inline bool
+xchk_bmap_has_next(
+	struct xchk_bmap_info	*info,
+	struct xfs_bmbt_irec	*irec)
+{
+	struct xfs_bmbt_irec	got;
+	struct xfs_ifork	*ifp;
+
+	ifp = xfs_ifork_ptr(info->sc->ip, info->whichfork);
+
+	if (!xfs_iext_peek_next_extent(ifp, &info->icur, &got))
+		return false;
+	if (irec->br_startoff + irec->br_blockcount != got.br_startoff)
+		return false;
+	if (irec->br_startblock + irec->br_blockcount != got.br_startblock)
+		return false;
+	if (got.br_state != irec->br_state)
+		return false;
+	return true;
+}
+
 /* Make sure that we have rmapbt records for this extent. */
 STATIC void
 xchk_bmap_xref_rmap(
@@ -214,6 +257,34 @@ xchk_bmap_xref_rmap(
 	if (rmap.rm_flags & XFS_RMAP_BMBT_BLOCK)
 		xchk_fblock_xref_set_corrupt(info->sc, info->whichfork,
 				irec->br_startoff);
+
+	/*
+	 * If the rmap starts before this bmbt record, make sure there's a bmbt
+	 * record for the previous offset that is contiguous with this mapping.
+	 * Skip this for CoW fork extents because the refcount btree (and not
+	 * the inode) is the ondisk owner for those extents.
+	 */
+	if (info->whichfork != XFS_COW_FORK && rmap.rm_startblock < agbno &&
+	    !xchk_bmap_has_prev(info, irec)) {
+		xchk_fblock_xref_set_corrupt(info->sc, info->whichfork,
+				irec->br_startoff);
+		return;
+	}
+
+	/*
+	 * If the rmap ends after this bmbt record, make sure there's a bmbt
+	 * record for the next offset that is contiguous with this mapping.
+	 * Skip this for CoW fork extents because the refcount btree (and not
+	 * the inode) is the ondisk owner for those extents.
+	 */
+	rmap_end = (unsigned long long)rmap.rm_startblock + rmap.rm_blockcount;
+	if (info->whichfork != XFS_COW_FORK &&
+	    rmap_end > agbno + irec->br_blockcount &&
+	    !xchk_bmap_has_next(info, irec)) {
+		xchk_fblock_xref_set_corrupt(info->sc, info->whichfork,
+				irec->br_startoff);
+		return;
+	}
 }
 
 /* Cross-reference a single rtdev extent record. */
@@ -626,7 +697,6 @@ xchk_bmap(
 	struct xfs_inode	*ip = sc->ip;
 	struct xfs_ifork	*ifp = xfs_ifork_ptr(ip, whichfork);
 	xfs_fileoff_t		endoff;
-	struct xfs_iext_cursor	icur;
 	int			error = 0;
 
 	/* Non-existent forks can be ignored. */
@@ -690,7 +760,7 @@ xchk_bmap(
 	/* Scrub extent records. */
 	info.lastoff = 0;
 	ifp = xfs_ifork_ptr(ip, whichfork);
-	for_each_xfs_iext(ifp, &icur, &irec) {
+	for_each_xfs_iext(ifp, &info.icur, &irec) {
 		if (xchk_should_terminate(sc, &error) ||
 		    (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT))
 			goto out;