dm: enable request based option

This patch enables request-based dm.

o Request-based dm and bio-based dm coexist, since there are
  some target drivers which are more fitting to bio-based dm.
  Also, there are other bio-based devices in the kernel
  (e.g. md, loop).
  Since bio-based device can't receive struct request,
  there are some limitations on device stacking between
  bio-based and request-based.

                     type of underlying device
                   bio-based      request-based
   ----------------------------------------------
    bio-based         OK                OK
    request-based     --                OK

  The device type is recognized by the queue flag in the kernel,
  so dm follows that.

o The type of a dm device is decided at the first table binding time.
  Once the type of a dm device is decided, the type can't be changed.

o Mempool allocations are deferred to at the table loading time, since
  mempools for request-based dm are different from those for bio-based
  dm and needed mempool type is fixed by the type of table.

o Currently, request-based dm supports only tables that have a single
  target.  To support multiple targets, we need to support request
  splitting or prevent bio/request from spanning multiple targets.
  The former needs lots of changes in the block layer, and the latter
  needs that all target drivers support merge() function.
  Both will take a time.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 111 insertions, 0 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index c5f784419f23..aaeb82ed2852 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -41,6 +41,7 @@
 struct dm_table {
         struct mapped_device *md;
         atomic_t holders;
+        unsigned type;
 
         /* btree table */
         unsigned int depth;
@@ -65,6 +66,8 @@ struct dm_table {
         /* events get handed up using this callback */
         void (*event_fn)(void *);
         void *event_context;
+
+        struct dm_md_mempools *mempools;
 };
 
 /*
@@ -258,6 +261,8 @@ void dm_table_destroy(struct dm_table *t)
         if (t->devices.next != &t->devices)
                 free_devices(&t->devices);
 
+        dm_free_md_mempools(t->mempools);
+
         kfree(t);
 }
 
@@ -764,6 +769,99 @@ int dm_table_add_target(struct dm_table *t, const char *type,
         return r;
 }
 
+int dm_table_set_type(struct dm_table *t)
+{
+        unsigned i;
+        unsigned bio_based = 0, request_based = 0;
+        struct dm_target *tgt;
+        struct dm_dev_internal *dd;
+        struct list_head *devices;
+
+        for (i = 0; i < t->num_targets; i++) {
+                tgt = t->targets + i;
+                if (dm_target_request_based(tgt))
+                        request_based = 1;
+                else
+                        bio_based = 1;
+
+                if (bio_based && request_based) {
+                        DMWARN("Inconsistent table: different target types"
+                               " can't be mixed up");
+                        return -EINVAL;
+                }
+        }
+
+        if (bio_based) {
+                /* We must use this table as bio-based */
+                t->type = DM_TYPE_BIO_BASED;
+                return 0;
+        }
+
+        BUG_ON(!request_based); /* No targets in this table */
+
+        /* Non-request-stackable devices can't be used for request-based dm */
+        devices = dm_table_get_devices(t);
+        list_for_each_entry(dd, devices, list) {
+                if (!blk_queue_stackable(bdev_get_queue(dd->dm_dev.bdev))) {
+                        DMWARN("table load rejected: including"
+                               " non-request-stackable devices");
+                        return -EINVAL;
+                }
+        }
+
+        /*
+         * Request-based dm supports only tables that have a single target now.
+         * To support multiple targets, request splitting support is needed,
+         * and that needs lots of changes in the block-layer.
+         * (e.g. request completion process for partial completion.)
+         */
+        if (t->num_targets > 1) {
+                DMWARN("Request-based dm doesn't support multiple targets yet");
+                return -EINVAL;
+        }
+
+        t->type = DM_TYPE_REQUEST_BASED;
+
+        return 0;
+}
+
+unsigned dm_table_get_type(struct dm_table *t)
+{
+        return t->type;
+}
+
+bool dm_table_request_based(struct dm_table *t)
+{
+        return dm_table_get_type(t) == DM_TYPE_REQUEST_BASED;
+}
+
+int dm_table_alloc_md_mempools(struct dm_table *t)
+{
+        unsigned type = dm_table_get_type(t);
+
+        if (unlikely(type == DM_TYPE_NONE)) {
+                DMWARN("no table type is set, can't allocate mempools");
+                return -EINVAL;
+        }
+
+        t->mempools = dm_alloc_md_mempools(type);
+        if (!t->mempools)
+                return -ENOMEM;
+
+        return 0;
+}
+
+void dm_table_free_md_mempools(struct dm_table *t)
+{
+        dm_free_md_mempools(t->mempools);
+        t->mempools = NULL;
+}
+
+struct dm_md_mempools *dm_table_get_md_mempools(struct dm_table *t)
+{
+        return t->mempools;
+}
+
 static int setup_indexes(struct dm_table *t)
 {
         int i;
@@ -985,6 +1083,19 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
                 queue_flag_set_unlocked(QUEUE_FLAG_CLUSTER, q);
 
         dm_table_set_integrity(t);
+
+        /*
+         * QUEUE_FLAG_STACKABLE must be set after all queue settings are
+         * visible to other CPUs because, once the flag is set, incoming bios
+         * are processed by request-based dm, which refers to the queue
+         * settings.
+         * Until the flag set, bios are passed to bio-based dm and queued to
+         * md->deferred where queue settings are not needed yet.
+         * Those bios are passed to request-based dm at the resume time.
+         */
+        smp_mb();
+        if (dm_table_request_based(t))
+                queue_flag_set_unlocked(QUEUE_FLAG_STACKABLE, q);
 }
 
 unsigned int dm_table_get_num_targets(struct dm_table *t)