xfs: only reserve quota blocks if we're mapping into a hole

When logging quota block count updates during a reflink operation, we
only log the /delta/ of the block count changes to the dquot.  Since we
now know ahead of time the extent type of both dmap and smap (and that
they have the same length), we know that we only need to reserve quota
blocks for dmap's blockcount if we're mapping it into a hole.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/xfs_reflink.c

@@ -1055,7 +1055,9 @@ xfs_reflink_remap_extent(
 	 *
 	 * If we are mapping a written extent into the file, we need to have
 	 * enough quota block count reservation to handle the blocks in that
-	 * extent.
+	 * extent.  We log only the delta to the quota block counts, so if the
+	 * extent we're unmapping also has blocks allocated to it, we don't
+	 * need a quota reservation for the extent itself.
 	 *
 	 * Note that if we're replacing a delalloc reservation with a written
 	 * extent, we have to take the full quota reservation because removing
@@ -1067,7 +1069,7 @@ xfs_reflink_remap_extent(
 	qres = qdelta = 0;
 	if (smap_real || dmap_written)
 		qres = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
-	if (dmap_written)
+	if (!smap_real && dmap_written)
 		qres += dmap->br_blockcount;
 	if (qres > 0) {
 		error = xfs_trans_reserve_quota_nblks(tp, ip, qres, 0,