dm: allow immutable request-based targets to use blk-mq pdu

This will allow DM multipath to use a portion of the blk-mq pdu space
for target data (e.g. struct dm_mpath_io).

Signed-off-by: Mike Snitzer <snitzer@redhat.com>

3 files changed, 28 insertions, 9 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 4763c4ae30e4..2adf81d81fca 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1304,7 +1304,7 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
                 dm_set_md_type(md, dm_table_get_type(t));
 
                 /* setup md->queue to reflect md's type (may block) */
-                r = dm_setup_md_queue(md);
+                r = dm_setup_md_queue(md, t);
                 if (r) {
                         DMWARN("unable to set up device queue for new table.");
                         goto err_unlock_md_type;
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 89aa9618c061..92c2fee413b6 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -224,7 +224,8 @@ struct mapped_device {
 
         /* for blk-mq request-based DM support */
         struct blk_mq_tag_set *tag_set;
-        bool use_blk_mq;
+        bool use_blk_mq:1;
+        bool init_tio_pdu:1;
 };
 
 #ifdef CONFIG_DM_MQ_DEFAULT
@@ -243,6 +244,7 @@ bool dm_use_blk_mq(struct mapped_device *md)
 {
         return md->use_blk_mq;
 }
+EXPORT_SYMBOL_GPL(dm_use_blk_mq);
 
 /*
  * For mempools pre-allocation at the table loading time.
@@ -1889,7 +1891,13 @@ static void init_tio(struct dm_rq_target_io *tio, struct request *rq,
         tio->clone = NULL;
         tio->orig = rq;
         tio->error = 0;
-        memset(&tio->info, 0, sizeof(tio->info));
+        /*
+         * Avoid initializing info for blk-mq; it passes
+         * target-specific data through info.ptr
+         * (see: dm_mq_init_request)
+         */
+        if (!md->init_tio_pdu)
+                memset(&tio->info, 0, sizeof(tio->info));
         if (md->kworker_task)
                 init_kthread_work(&tio->work, map_tio_request);
 }
@@ -2313,6 +2321,7 @@ static struct mapped_device *alloc_dev(int minor)
                 goto bad_io_barrier;
 
         md->use_blk_mq = use_blk_mq;
+        md->init_tio_pdu = false;
         md->type = DM_TYPE_NONE;
         mutex_init(&md->suspend_lock);
         mutex_init(&md->type_lock);
@@ -2653,6 +2662,11 @@ static int dm_mq_init_request(void *data, struct request *rq,
          */
         tio->md = md;
 
+        if (md->init_tio_pdu) {
+                /* target-specific per-io data is immediately after the tio */
+                tio->info.ptr = tio + 1;
+        }
+
         return 0;
 }
 
@@ -2704,7 +2718,8 @@ static struct blk_mq_ops dm_mq_ops = {
         .init_request = dm_mq_init_request,
 };
 
-static int dm_mq_init_request_queue(struct mapped_device *md)
+static int dm_mq_init_request_queue(struct mapped_device *md,
+                                    struct dm_target *immutable_tgt)
 {
         struct request_queue *q;
         int err;
@@ -2726,6 +2741,11 @@ static int dm_mq_init_request_queue(struct mapped_device *md)
         md->tag_set->driver_data = md;
 
         md->tag_set->cmd_size = sizeof(struct dm_rq_target_io);
+        if (immutable_tgt && immutable_tgt->per_io_data_size) {
+                /* any target-specific per-io data is immediately after the tio */
+                md->tag_set->cmd_size += immutable_tgt->per_io_data_size;
+                md->init_tio_pdu = true;
+        }
 
         err = blk_mq_alloc_tag_set(md->tag_set);
         if (err)
@@ -2763,7 +2783,7 @@ static unsigned filter_md_type(unsigned type, struct mapped_device *md)
 /*
  * Setup the DM device's queue based on md's type
  */
-int dm_setup_md_queue(struct mapped_device *md)
+int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
 {
         int r;
         unsigned md_type = filter_md_type(dm_get_md_type(md), md);
@@ -2777,7 +2797,7 @@ int dm_setup_md_queue(struct mapped_device *md)
                 }
                 break;
         case DM_TYPE_MQ_REQUEST_BASED:
-                r = dm_mq_init_request_queue(md);
+                r = dm_mq_init_request_queue(md, dm_table_get_immutable_target(t));
                 if (r) {
                         DMERR("Cannot initialize queue for request-based dm-mq mapped device");
                         return r;
@@ -3505,8 +3525,7 @@ struct dm_md_mempools *dm_alloc_md_mempools(struct mapped_device *md, unsigned t
                 if (!pool_size)
                         pool_size = dm_get_reserved_rq_based_ios();
                 front_pad = offsetof(struct dm_rq_clone_bio_info, clone);
-                /* per_io_data_size is not used. */
-                WARN_ON(per_io_data_size != 0);
+                /* per_io_data_size is used for blk-mq pdu at queue allocation */
                 break;
         default:
                 BUG();
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 4305a513c801..13a758ec0f88 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -86,7 +86,7 @@ void dm_set_md_type(struct mapped_device *md, unsigned type);
 unsigned dm_get_md_type(struct mapped_device *md);
 struct target_type *dm_get_immutable_target_type(struct mapped_device *md);
 
-int dm_setup_md_queue(struct mapped_device *md);
+int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t);
 
 /*
  * To check the return value from dm_table_find_target().