dm mpath: add optional "queue_mode" feature

Allow a user to specify an optional feature 'queue_mode <mode>' where
<mode> may be "bio", "rq" or "mq" -- which corresponds to bio-based,
request_fn rq-based, and blk-mq rq-based respectively.

If the queue_mode feature isn't specified the default for the
"multipath" target is still "rq" but if dm_mod.use_blk_mq is set to Y
it'll default to mode "mq".

This new queue_mode feature introduces the ability for each multipath
device to have its own queue_mode (whereas before this feature all
multipath devices effectively had to have the same queue_mode).

This commit also goes a long way to eliminate the awkward (ab)use of
DM_TYPE_*, the associated filter_md_type() and other relatively fragile
and difficult to maintain code.

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

1 files changed, 80 insertions, 69 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 2d10ff780d84..7eac080fcb18 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -90,6 +90,8 @@ struct multipath {
         atomic_t pg_init_in_progress;   /* Only one pg_init allowed at once */
         atomic_t pg_init_count;         /* Number of times pg_init called */
 
+        unsigned queue_mode;
+
         /*
          * We must use a mempool of dm_mpath_io structs so that we
          * can resubmit bios on error.
@@ -131,7 +133,6 @@ static void process_queued_bios(struct work_struct *work);
 #define MPATHF_PG_INIT_DISABLED 4               /* pg_init is not currently allowed */
 #define MPATHF_PG_INIT_REQUIRED 5               /* pg_init needs calling? */
 #define MPATHF_PG_INIT_DELAY_RETRY 6            /* Delay pg_init retry? */
-#define MPATHF_BIO_BASED 7                      /* Device is bio-based? */
 
 /*-----------------------------------------------
  * Allocation routines
@@ -191,8 +192,7 @@ static void free_priority_group(struct priority_group *pg,
         kfree(pg);
 }
 
-static struct multipath *alloc_multipath(struct dm_target *ti, bool use_blk_mq,
-                                         bool bio_based)
+static struct multipath *alloc_multipath(struct dm_target *ti)
 {
         struct multipath *m;
 
@@ -210,25 +210,7 @@ static struct multipath *alloc_multipath(struct dm_target *ti, bool use_blk_mq,
                 mutex_init(&m->work_mutex);
 
                 m->mpio_pool = NULL;
-                if (!use_blk_mq && !bio_based) {
-                        unsigned min_ios = dm_get_reserved_rq_based_ios();
-
-                        m->mpio_pool = mempool_create_slab_pool(min_ios, _mpio_cache);
-                        if (!m->mpio_pool) {
-                                kfree(m);
-                                return NULL;
-                        }
-                }
-
-                if (bio_based) {
-                        INIT_WORK(&m->process_queued_bios, process_queued_bios);
-                        set_bit(MPATHF_BIO_BASED, &m->flags);
-                        /*
-                         * bio-based doesn't support any direct scsi_dh management;
-                         * it just discovers if a scsi_dh is attached.
-                         */
-                        set_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags);
-                }
+                m->queue_mode = DM_TYPE_NONE;
 
                 m->ti = ti;
                 ti->private = m;
@@ -237,6 +219,39 @@ static struct multipath *alloc_multipath(struct dm_target *ti, bool use_blk_mq,
         return m;
 }
 
+static int alloc_multipath_stage2(struct dm_target *ti, struct multipath *m)
+{
+        if (m->queue_mode == DM_TYPE_NONE) {
+                /*
+                 * Default to request-based.
+                 */
+                if (dm_use_blk_mq(dm_table_get_md(ti->table)))
+                        m->queue_mode = DM_TYPE_MQ_REQUEST_BASED;
+                else
+                        m->queue_mode = DM_TYPE_REQUEST_BASED;
+        }
+
+        if (m->queue_mode == DM_TYPE_REQUEST_BASED) {
+                unsigned min_ios = dm_get_reserved_rq_based_ios();
+
+                m->mpio_pool = mempool_create_slab_pool(min_ios, _mpio_cache);
+                if (!m->mpio_pool)
+                        return -ENOMEM;
+        }
+        else if (m->queue_mode == DM_TYPE_BIO_BASED) {
+                INIT_WORK(&m->process_queued_bios, process_queued_bios);
+                /*
+                 * bio-based doesn't support any direct scsi_dh management;
+                 * it just discovers if a scsi_dh is attached.
+                 */
+                set_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags);
+        }
+
+        dm_table_set_type(ti->table, m->queue_mode);
+
+        return 0;
+}
+
 static void free_multipath(struct multipath *m)
 {
         struct priority_group *pg, *tmp;
@@ -653,7 +668,7 @@ static int multipath_map_bio(struct dm_target *ti, struct bio *bio)
 
 static void process_queued_bios_list(struct multipath *m)
 {
-        if (test_bit(MPATHF_BIO_BASED, &m->flags))
+        if (m->queue_mode == DM_TYPE_BIO_BASED)
                 queue_work(kmultipathd, &m->process_queued_bios);
 }
 
@@ -964,7 +979,7 @@ static int parse_hw_handler(struct dm_arg_set *as, struct multipath *m)
         if (!hw_argc)
                 return 0;
 
-        if (test_bit(MPATHF_BIO_BASED, &m->flags)) {
+        if (m->queue_mode == DM_TYPE_BIO_BASED) {
                 dm_consume_args(as, hw_argc);
                 DMERR("bio-based multipath doesn't allow hardware handler args");
                 return 0;
@@ -1005,7 +1020,7 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
         const char *arg_name;
 
         static struct dm_arg _args[] = {
-                {0, 6, "invalid number of feature args"},
+                {0, 8, "invalid number of feature args"},
                 {1, 50, "pg_init_retries must be between 1 and 50"},
                 {0, 60000, "pg_init_delay_msecs must be between 0 and 60000"},
         };
@@ -1045,6 +1060,24 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
                         continue;
                 }
 
+                if (!strcasecmp(arg_name, "queue_mode") &&
+                    (argc >= 1)) {
+                        const char *queue_mode_name = dm_shift_arg(as);
+
+                        if (!strcasecmp(queue_mode_name, "bio"))
+                                m->queue_mode = DM_TYPE_BIO_BASED;
+                        else if (!strcasecmp(queue_mode_name, "rq"))
+                                m->queue_mode = DM_TYPE_REQUEST_BASED;
+                        else if (!strcasecmp(queue_mode_name, "mq"))
+                                m->queue_mode = DM_TYPE_MQ_REQUEST_BASED;
+                        else {
+                                ti->error = "Unknown 'queue_mode' requested";
+                                r = -EINVAL;
+                        }
+                        argc--;
+                        continue;
+                }
+
                 ti->error = "Unrecognised multipath feature request";
                 r = -EINVAL;
         } while (argc && !r);
@@ -1052,8 +1085,7 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
         return r;
 }
 
-static int __multipath_ctr(struct dm_target *ti, unsigned int argc,
-                           char **argv, bool bio_based)
+static int multipath_ctr(struct dm_target *ti, unsigned argc, char **argv)
 {
         /* target arguments */
         static struct dm_arg _args[] = {
@@ -1066,12 +1098,11 @@ static int __multipath_ctr(struct dm_target *ti, unsigned int argc,
         struct dm_arg_set as;
         unsigned pg_count = 0;
         unsigned next_pg_num;
-        bool use_blk_mq = dm_use_blk_mq(dm_table_get_md(ti->table));
 
         as.argc = argc;
         as.argv = argv;
 
-        m = alloc_multipath(ti, use_blk_mq, bio_based);
+        m = alloc_multipath(ti);
         if (!m) {
                 ti->error = "can't allocate multipath";
                 return -EINVAL;
@@ -1081,6 +1112,10 @@ static int __multipath_ctr(struct dm_target *ti, unsigned int argc,
         if (r)
                 goto bad;
 
+        r = alloc_multipath_stage2(ti, m);
+        if (r)
+                goto bad;
+
         r = parse_hw_handler(&as, m);
         if (r)
                 goto bad;
@@ -1130,9 +1165,9 @@ static int __multipath_ctr(struct dm_target *ti, unsigned int argc,
         ti->num_flush_bios = 1;
         ti->num_discard_bios = 1;
         ti->num_write_same_bios = 1;
-        if (bio_based)
+        if (m->queue_mode == DM_TYPE_BIO_BASED)
                 ti->per_io_data_size = multipath_per_bio_data_size();
-        else if (use_blk_mq)
+        else if (m->queue_mode == DM_TYPE_MQ_REQUEST_BASED)
                 ti->per_io_data_size = sizeof(struct dm_mpath_io);
 
         return 0;
@@ -1142,16 +1177,6 @@ static int __multipath_ctr(struct dm_target *ti, unsigned int argc,
         return r;
 }
 
-static int multipath_ctr(struct dm_target *ti, unsigned argc, char **argv)
-{
-        return __multipath_ctr(ti, argc, argv, false);
-}
-
-static int multipath_bio_ctr(struct dm_target *ti, unsigned argc, char **argv)
-{
-        return __multipath_ctr(ti, argc, argv, true);
-}
-
 static void multipath_wait_for_pg_init_completion(struct multipath *m)
 {
         DECLARE_WAITQUEUE(wait, current);
@@ -1700,7 +1725,9 @@ static void multipath_status(struct dm_target *ti, status_type_t type,
                 DMEMIT("%u ", test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags) +
                               (m->pg_init_retries > 0) * 2 +
                               (m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT) * 2 +
-                              test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags));
+                              test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags) +
+                              (m->queue_mode != DM_TYPE_REQUEST_BASED) * 2);
+
                 if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))
                         DMEMIT("queue_if_no_path ");
                 if (m->pg_init_retries)
@@ -1709,6 +1736,16 @@ static void multipath_status(struct dm_target *ti, status_type_t type,
                         DMEMIT("pg_init_delay_msecs %u ", m->pg_init_delay_msecs);
                 if (test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags))
                         DMEMIT("retain_attached_hw_handler ");
+                if (m->queue_mode != DM_TYPE_REQUEST_BASED) {
+                        switch(m->queue_mode) {
+                        case DM_TYPE_BIO_BASED:
+                                DMEMIT("queue_mode bio ");
+                                break;
+                        case DM_TYPE_MQ_REQUEST_BASED:
+                                DMEMIT("queue_mode mq ");
+                                break;
+                        }
+                }
         }
 
         if (!m->hw_handler_name || type == STATUSTYPE_INFO)
@@ -1995,7 +2032,7 @@ static int multipath_busy(struct dm_target *ti)
  *---------------------------------------------------------------*/
 static struct target_type multipath_target = {
         .name = "multipath",
-        .version = {1, 11, 0},
+        .version = {1, 12, 0},
         .features = DM_TARGET_SINGLETON | DM_TARGET_IMMUTABLE,
         .module = THIS_MODULE,
         .ctr = multipath_ctr,
@@ -2004,22 +2041,6 @@ static struct target_type multipath_target = {
         .clone_and_map_rq = multipath_clone_and_map,
         .release_clone_rq = multipath_release_clone,
         .rq_end_io = multipath_end_io,
-        .presuspend = multipath_presuspend,
-        .postsuspend = multipath_postsuspend,
-        .resume = multipath_resume,
-        .status = multipath_status,
-        .message = multipath_message,
-        .prepare_ioctl = multipath_prepare_ioctl,
-        .iterate_devices = multipath_iterate_devices,
-        .busy = multipath_busy,
-};
-
-static struct target_type multipath_bio_target = {
-        .name = "multipath-bio",
-        .version = {1, 0, 0},
-        .module = THIS_MODULE,
-        .ctr = multipath_bio_ctr,
-        .dtr = multipath_dtr,
         .map = multipath_map_bio,
         .end_io = multipath_end_io_bio,
         .presuspend = multipath_presuspend,
@@ -2048,13 +2069,6 @@ static int __init dm_multipath_init(void)
                 goto bad_register_target;
         }
 
-        r = dm_register_target(&multipath_bio_target);
-        if (r < 0) {
-                DMERR("bio-based register failed %d", r);
-                r = -EINVAL;
-                goto bad_register_bio_based_target;
-        }
-
         kmultipathd = alloc_workqueue("kmpathd", WQ_MEM_RECLAIM, 0);
         if (!kmultipathd) {
                 DMERR("failed to create workqueue kmpathd");
@@ -2081,8 +2095,6 @@ static int __init dm_multipath_init(void)
 bad_alloc_kmpath_handlerd:
         destroy_workqueue(kmultipathd);
 bad_alloc_kmultipathd:
-        dm_unregister_target(&multipath_bio_target);
-bad_register_bio_based_target:
         dm_unregister_target(&multipath_target);
 bad_register_target:
         kmem_cache_destroy(_mpio_cache);
@@ -2096,7 +2108,6 @@ static void __exit dm_multipath_exit(void)
         destroy_workqueue(kmultipathd);
 
         dm_unregister_target(&multipath_target);
-        dm_unregister_target(&multipath_bio_target);
         kmem_cache_destroy(_mpio_cache);
 }