reshape: support raid5 grow on certain older kernels.

Kernels between
  c6563a8c38fde3c1c7fc925a v3.5-rc1~110^2~53
and
  b5254dd5fdd9abcacadb5101 v3.5-rc1~110^2~51

allow new_offset to be set, but don't then allow a RAID5
to be reshaped to change that offset.
Due to selective backports, this includes the SLES11-SP3 kernel.

It is quite easy to handle this case in mdadm, so we do.
Specifically: if the reshape with data-offset fails with EINVAL,
abort the data-offset change and try the "old" way.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 13 insertions, 2 deletions

diff --git a/Grow.c b/Grow.c
index a8bbf2b..9a573fd 100644
--- a/Grow.c
+++ b/Grow.c
@@ -3102,8 +3102,19 @@ static int reshape_array(char *container, int fd, char *devname,
 				   devname, container, &reshape) < 0)
 			goto release;
 		if (sysfs_set_str(sra, NULL, "sync_action", "reshape") < 0) {
-			pr_err("Failed to initiate reshape!\n");
-			goto release;
+			struct mdinfo *sd;
+			if (errno != EINVAL) {
+				pr_err("Failed to initiate reshape!\n");
+				goto release;
+			}
+			/* revert data_offset and try the old way */
+			for (sd = sra->devs; sd; sd = sd->next) {
+				sysfs_set_num(sra, sd, "new_offset",
+					      sd->data_offset);
+				sysfs_set_str(sra, NULL, "reshape_direction",
+					      "forwards");
+			}
+			break;
 		}
 		if (info->new_level == reshape.level)
 			return 0;