dm: allow error target to replace bio-based and request-based targets

It may be useful to switch a request-based table to the "error" target.
Enhance the DM core to allow a hybrid target_type which is capable of
handling either bios (via .map) or requests (via .map_rq).

Add a request-based map function (.map_rq) to the "error" target_type;
making it DM's first hybrid target.  Train dm_table_set_type() to prefer
the mapped device's established type (request-based or bio-based).  If
the mapped device doesn't have an established type default to making the
table with the hybrid target(s) bio-based.

Tested 'dmsetup wipe_table' to work on both bio-based and request-based
devices.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Joe Jin <joe.jin@oracle.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 45b97da1bd0..8b4c075d9a2 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -89,10 +89,21 @@ int dm_setup_md_queue(struct mapped_device *md);
 #define dm_target_is_valid(t) ((t)->table)
 
 /*
+ * To check whether the target type is bio-based or not (request-based).
+ */
+#define dm_target_bio_based(t) ((t)->type->map != NULL)
+
+/*
  * To check whether the target type is request-based or not (bio-based).
  */
 #define dm_target_request_based(t) ((t)->type->map_rq != NULL)
 
+/*
+ * To check whether the target type is a hybrid (capable of being
+ * either request-based or bio-based).
+ */
+#define dm_target_hybrid(t) (dm_target_bio_based(t) && dm_target_request_based(t))
+
 /*-----------------------------------------------------------------
  * A registry of target types.
  *---------------------------------------------------------------*/