[PATCH] md: set desc_nr correctly for version-1 superblocks

This has to be done in ->load_super, not ->validate_super

Without this, hot-adding devices to an array doesn't always
work right - though there is a work around in mdadm-2.5.2 to
make this less of an issue.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/md/md.c b/drivers/md/md.c
index e4e1613..9f76e0c 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1062,6 +1062,11 @@
 	if (rdev->sb_size & bmask)
 		rdev-> sb_size = (rdev->sb_size | bmask)+1;
 
+	if (sb->level == cpu_to_le32(LEVEL_MULTIPATH))
+		rdev->desc_nr = -1;
+	else
+		rdev->desc_nr = le32_to_cpu(sb->dev_number);
+
 	if (refdev == 0)
 		ret = 1;
 	else {
@@ -1171,7 +1176,6 @@
 	}
 	if (mddev->level != LEVEL_MULTIPATH) {
 		int role;
-		rdev->desc_nr = le32_to_cpu(sb->dev_number);
 		role = le16_to_cpu(sb->dev_roles[rdev->desc_nr]);
 		switch(role) {
 		case 0xffff: /* spare */