xfs: teach xfs_bmapi_remap to accept some bmapi flags

Teach xfs_bmapi_remap how to map in unwritten extent and to skip rmap
updates.  This enables us to rebuild real and unwritten extents from the
rmapbt.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/libxfs/xfs_bmap.c

@@ -4543,7 +4543,10 @@ xfs_bmapi_remap(
 	ASSERT(len > 0);
 	ASSERT(len <= (xfs_filblks_t)MAXEXTLEN);
 	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
-	ASSERT(!(flags & ~(XFS_BMAPI_ATTRFORK)));
+	ASSERT(!(flags & ~(XFS_BMAPI_ATTRFORK | XFS_BMAPI_PREALLOC |
+			   XFS_BMAPI_NORMAP)));
+	ASSERT((flags & (XFS_BMAPI_ATTRFORK | XFS_BMAPI_PREALLOC)) !=
+			(XFS_BMAPI_ATTRFORK | XFS_BMAPI_PREALLOC));
 
 	if (unlikely(XFS_TEST_ERROR(
 	    (XFS_IFORK_FORMAT(ip, whichfork) != XFS_DINODE_FMT_EXTENTS &&
@@ -4581,7 +4584,10 @@ xfs_bmapi_remap(
 	got.br_startoff = bno;
 	got.br_startblock = startblock;
 	got.br_blockcount = len;
-	got.br_state = XFS_EXT_NORM;
+	if (flags & XFS_BMAPI_PREALLOC)
+		got.br_state = XFS_EXT_UNWRITTEN;
+	else
+		got.br_state = XFS_EXT_NORM;
 
 	error = xfs_bmap_add_extent_hole_real(tp, ip, whichfork, &icur,
 			&cur, &got, &firstblock, dfops, &logflags, flags);