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, 8 insertions, 1 deletions

diff --git a/drivers/md/dm-target.c b/drivers/md/dm-target.c
index 37ba5db71cd9..242e3cec397a 100644
--- a/drivers/md/dm-target.c
+++ b/drivers/md/dm-target.c
@@ -131,12 +131,19 @@ static int io_err_map(struct dm_target *tt, struct bio *bio)
         return -EIO;
 }
 
+static int io_err_map_rq(struct dm_target *ti, struct request *clone,
+                         union map_info *map_context)
+{
+        return -EIO;
+}
+
 static struct target_type error_target = {
         .name = "error",
-        .version = {1, 1, 0},
+        .version = {1, 2, 0},
         .ctr  = io_err_ctr,
         .dtr  = io_err_dtr,
         .map  = io_err_map,
+        .map_rq = io_err_map_rq,
 };
 
 int __init dm_target_init(void)