xfs: have getfsmap fall back to the freesp btrees when rmap is not present

If the reverse-mapping btree isn't available, fall back to the
free space btrees to provide partial reverse mapping information.
The online scrub tool can make use of even partial information to
speed up the data block scan.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/xfs_fsmap.c

@@ -40,6 +40,7 @@
 #include "xfs_fsmap.h"
 #include "xfs_refcount.h"
 #include "xfs_refcount_btree.h"
+#include "xfs_alloc_btree.h"
 
 /* Convert an xfs_fsmap to an fsmap. */
 void
@@ -158,6 +159,9 @@ xfs_fsmap_owner_from_rmap(
 	case XFS_RMAP_OWN_COW:
 		dest->fmr_owner = XFS_FMR_OWN_COW;
 		break;
+	case XFS_RMAP_OWN_NULL:	/* "free" */
+		dest->fmr_owner = XFS_FMR_OWN_FREE;
+		break;
 	default:
 		return -EFSCORRUPTED;
 	}
@@ -362,6 +366,30 @@ xfs_getfsmap_datadev_helper(
 	return xfs_getfsmap_helper(cur->bc_tp, info, rec, rec_daddr);
 }
 
+/* Transform a bnobt irec into a fsmap */
+STATIC int
+xfs_getfsmap_datadev_bnobt_helper(
+	struct xfs_btree_cur		*cur,
+	struct xfs_alloc_rec_incore	*rec,
+	void				*priv)
+{
+	struct xfs_mount		*mp = cur->bc_mp;
+	struct xfs_getfsmap_info	*info = priv;
+	struct xfs_rmap_irec		irec;
+	xfs_daddr_t			rec_daddr;
+
+	rec_daddr = XFS_AGB_TO_DADDR(mp, cur->bc_private.a.agno,
+			rec->ar_startblock);
+
+	irec.rm_startblock = rec->ar_startblock;
+	irec.rm_blockcount = rec->ar_blockcount;
+	irec.rm_owner = XFS_RMAP_OWN_NULL;	/* "free" */
+	irec.rm_offset = 0;
+	irec.rm_flags = 0;
+
+	return xfs_getfsmap_helper(cur->bc_tp, info, &irec, rec_daddr);
+}
+
 /* Set rmap flags based on the getfsmap flags */
 static void
 xfs_getfsmap_set_irec_flags(
@@ -572,6 +600,43 @@ xfs_getfsmap_datadev_rmapbt(
 			xfs_getfsmap_datadev_rmapbt_query, NULL);
 }
 
+/* Actually query the bno btree. */
+STATIC int
+xfs_getfsmap_datadev_bnobt_query(
+	struct xfs_trans		*tp,
+	struct xfs_getfsmap_info	*info,
+	struct xfs_btree_cur		**curpp,
+	void				*priv)
+{
+	struct xfs_alloc_rec_incore	*key = priv;
+
+	/* Report any gap at the end of the last AG. */
+	if (info->last)
+		return xfs_getfsmap_datadev_bnobt_helper(*curpp, &key[1], info);
+
+	/* Allocate cursor for this AG and query_range it. */
+	*curpp = xfs_allocbt_init_cursor(tp->t_mountp, tp, info->agf_bp,
+			info->agno, XFS_BTNUM_BNO);
+	key->ar_startblock = info->low.rm_startblock;
+	key[1].ar_startblock = info->high.rm_startblock;
+	return xfs_alloc_query_range(*curpp, key, &key[1],
+			xfs_getfsmap_datadev_bnobt_helper, info);
+}
+
+/* Execute a getfsmap query against the regular data device's bnobt. */
+STATIC int
+xfs_getfsmap_datadev_bnobt(
+	struct xfs_trans		*tp,
+	struct xfs_fsmap		*keys,
+	struct xfs_getfsmap_info	*info)
+{
+	struct xfs_alloc_rec_incore	akeys[2];
+
+	info->missing_owner = XFS_FMR_OWN_UNKNOWN;
+	return __xfs_getfsmap_datadev(tp, keys, info,
+			xfs_getfsmap_datadev_bnobt_query, &akeys[0]);
+}
+
 /* Do we recognize the device? */
 STATIC bool
 xfs_getfsmap_is_valid_device(
@@ -652,8 +717,6 @@ xfs_getfsmap(
 	int				i;
 	int				error = 0;
 
-	if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
-		return -EOPNOTSUPP;
 	if (head->fmh_iflags & ~FMH_IF_VALID)
 		return -EINVAL;
 	if (!xfs_getfsmap_is_valid_device(mp, &head->fmh_keys[0]) ||
@@ -665,7 +728,10 @@ xfs_getfsmap(
 	/* Set up our device handlers. */
 	memset(handlers, 0, sizeof(handlers));
 	handlers[0].dev = new_encode_dev(mp->m_ddev_targp->bt_dev);
-	handlers[0].fn = xfs_getfsmap_datadev_rmapbt;
+	if (xfs_sb_version_hasrmapbt(&mp->m_sb))
+		handlers[0].fn = xfs_getfsmap_datadev_rmapbt;
+	else
+		handlers[0].fn = xfs_getfsmap_datadev_bnobt;
 	if (mp->m_logdev_targp != mp->m_ddev_targp) {
 		handlers[1].dev = new_encode_dev(mp->m_logdev_targp->bt_dev);
 		handlers[1].fn = xfs_getfsmap_logdev;