From: Hannes Reinecke <hare@suse.de>
Subject: Emulate BLKRRPART on device-mapper
Patch-mainline: not yet

Partitions on device-mapper devices are managed by kpartx (if at
all). So if we were just to send out a 'change' event if someone
called BLKRRPART on these devices, kpartx will be triggered via udev
and can manage the partitions accordingly.

Signed-off-by: Hannes Reinecke <hare@suse.de>

---
 drivers/md/dm.c |   22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -421,19 +421,25 @@ static int dm_blk_ioctl(struct block_dev
 	if (!map || !dm_table_get_size(map))
 		goto out;
 
-	/* We only support devices that have a single target */
-	if (dm_table_get_num_targets(map) != 1)
-		goto out;
-
-	tgt = dm_table_get_target(map, 0);
-
 	if (dm_suspended_md(md)) {
 		r = -EAGAIN;
 		goto out;
 	}
 
-	if (tgt->type->ioctl)
-		r = tgt->type->ioctl(tgt, cmd, arg);
+	if (cmd == BLKRRPART) {
+		/* Emulate Re-read partitions table */
+		kobject_uevent(&disk_to_dev(md->disk)->kobj, KOBJ_CHANGE);
+		r = 0;
+	} else {
+		/* We only support devices that have a single target */
+		if (dm_table_get_num_targets(map) != 1)
+			goto out;
+
+		tgt = dm_table_get_target(map, 0);
+
+		if (tgt->type->ioctl)
+			r = tgt->type->ioctl(tgt, cmd, arg);
+	}
 
 out:
 	dm_table_put(map);
