[PATCH 18/53] xfs: don't update rmapbt when fixing agfl

[Darrick J. Wong]

Allow a caller of xfs_alloc_fix_freelist to disable rmapbt updates
when fixing the AG freelist.  xfs_repair needs this during phase 5
to be able to adjust the freelist while it's reconstructing the rmap
btree; the missing entries will be added back at the very end of
phase 5 once the AGFL contents settle down.

Signed-off-by: Darrick J. Wong <darrick.wong at oracle.com>
---
 libxfs/xfs_alloc.c |   40 ++++++++++++++++++++++++++--------------
 libxfs/xfs_alloc.h |    2 ++
 2 files changed, 28 insertions(+), 14 deletions(-)


diff --git a/libxfs/xfs_alloc.c b/libxfs/xfs_alloc.c
index 6c2b991..fd0767e 100644
--- a/libxfs/xfs_alloc.c
+++ b/libxfs/xfs_alloc.c
@@ -2098,26 +2098,38 @@ xfs_alloc_fix_freelist(
 	 * anything other than extra overhead when we need to put more blocks
 	 * back on the free list? Maybe we should only do this when space is
 	 * getting low or the AGFL is more than half full?
+	 *
+	 * The NOSHRINK flag prevents the AGFL from being shrunk if it's too
+	 * big; the NORMAP flag prevents AGFL expand/shrink operations from
+	 * updating the rmapbt.  Both flags are used in xfs_repair while we're
+	 * rebuilding the rmapbt, and neither are used by the kernel.  They're
+	 * both required to ensure that rmaps are correctly recorded for the
+	 * regenerated AGFL, bnobt, and cntbt.  See repair/phase5.c and
+	 * repair/rmap.c in xfsprogs for details.
 	 */
-	XFS_RMAP_AG_OWNER(&targs.oinfo, XFS_RMAP_OWN_AG);
-	while (pag->pagf_flcount > need) {
-		struct xfs_buf	*bp;
+	memset(&targs, 0, sizeof(targs));
+	if (!(flags & XFS_ALLOC_FLAG_NOSHRINK)) {
+		if (!(flags & XFS_ALLOC_FLAG_NORMAP))
+			XFS_RMAP_AG_OWNER(&targs.oinfo, XFS_RMAP_OWN_AG);
+		while (pag->pagf_flcount > need) {
+			struct xfs_buf	*bp;
 
-		error = xfs_alloc_get_freelist(tp, agbp, &bno, 0);
-		if (error)
-			goto out_agbp_relse;
-		error = xfs_free_ag_extent(tp, agbp, args->agno, bno, 1,
-					   &targs.oinfo, 1);
-		if (error)
-			goto out_agbp_relse;
-		bp = xfs_btree_get_bufs(mp, tp, args->agno, bno, 0);
-		xfs_trans_binval(tp, bp);
+			error = xfs_alloc_get_freelist(tp, agbp, &bno, 0);
+			if (error)
+				goto out_agbp_relse;
+			error = xfs_free_ag_extent(tp, agbp, args->agno, bno, 1,
+						   &targs.oinfo, 1);
+			if (error)
+				goto out_agbp_relse;
+			bp = xfs_btree_get_bufs(mp, tp, args->agno, bno, 0);
+			xfs_trans_binval(tp, bp);
+		}
 	}
 
-	memset(&targs, 0, sizeof(targs));
 	targs.tp = tp;
 	targs.mp = mp;
-	XFS_RMAP_AG_OWNER(&targs.oinfo, XFS_RMAP_OWN_AG);
+	if (!(flags & XFS_ALLOC_FLAG_NORMAP))
+		XFS_RMAP_AG_OWNER(&targs.oinfo, XFS_RMAP_OWN_AG);
 	targs.agbp = agbp;
 	targs.agno = args->agno;
 	targs.alignment = targs.minlen = targs.prod = targs.isfl = 1;
diff --git a/libxfs/xfs_alloc.h b/libxfs/xfs_alloc.h
index f78ce53..754b5dd 100644
--- a/libxfs/xfs_alloc.h
+++ b/libxfs/xfs_alloc.h
@@ -54,6 +54,8 @@ typedef unsigned int xfs_alloctype_t;
  */
 #define	XFS_ALLOC_FLAG_TRYLOCK	0x00000001  /* use trylock for buffer locking */
 #define	XFS_ALLOC_FLAG_FREEING	0x00000002  /* indicate caller is freeing extents*/
+#define	XFS_ALLOC_FLAG_NORMAP	0x00000004  /* don't modify the rmapbt */
+#define	XFS_ALLOC_FLAG_NOSHRINK	0x00000008  /* don't shrink the freelist */
 
 
 /*