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>

3 files changed, 39 insertions, 3 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index f221812b7dbc..f309477d7efe 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -860,14 +860,17 @@ EXPORT_SYMBOL(dm_consume_args);
 static int dm_table_set_type(struct dm_table *t)
 {
         unsigned i;
-        unsigned bio_based = 0, request_based = 0;
+        unsigned bio_based = 0, request_based = 0, hybrid = 0;
         struct dm_target *tgt;
         struct dm_dev_internal *dd;
         struct list_head *devices;
+        unsigned live_md_type;
 
         for (i = 0; i < t->num_targets; i++) {
                 tgt = t->targets + i;
-                if (dm_target_request_based(tgt))
+                if (dm_target_hybrid(tgt))
+                        hybrid = 1;
+                else if (dm_target_request_based(tgt))
                         request_based = 1;
                 else
                         bio_based = 1;
@@ -879,6 +882,21 @@ static int dm_table_set_type(struct dm_table *t)
                 }
         }
 
+        if (hybrid && !bio_based && !request_based) {
+                /*
+                 * The targets can work either way.
+                 * Determine the type from the live device.
+                 * Default to bio-based if device is new.
+                 */
+                dm_lock_md_type(t->md);
+                live_md_type = dm_get_md_type(t->md);
+                dm_unlock_md_type(t->md);
+                if (live_md_type == DM_TYPE_REQUEST_BASED)
+                        request_based = 1;
+                else
+                        bio_based = 1;
+        }
+
         if (bio_based) {
                 /* We must use this table as bio-based */
                 t->type = DM_TYPE_BIO_BASED;
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)
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 45b97da1bd06..8b4c075d9a2f 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.
  *---------------------------------------------------------------*/