block: allow initialization of previously allocated request_queue

blk_init_queue() allocates the request_queue structure and then
initializes it as needed (request_fn, elevator, etc).

Split initialization out to blk_init_allocated_queue_node.
Introduce blk_init_allocated_queue wrapper function to model existing
blk_init_queue and blk_init_queue_node interfaces.

Export elv_register_queue to allow a newly added elevator to be
registered with sysfs.  Export elv_unregister_queue for symmetry.

These changes allow DM to initialize a device's request_queue with more
precision.  In particular, DM no longer unconditionally initializes a
full request_queue (elevator et al).  It only does so for a
request-based DM device.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

2 files changed, 19 insertions, 1 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index e9a5ae25db8c..3bc5579d6f54 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -572,6 +572,22 @@ blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
 {
         struct request_queue *q = blk_alloc_queue_node(GFP_KERNEL, node_id);
 
+        return blk_init_allocated_queue_node(q, rfn, lock, node_id);
+}
+EXPORT_SYMBOL(blk_init_queue_node);
+
+struct request_queue *
+blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
+                         spinlock_t *lock)
+{
+        return blk_init_allocated_queue_node(q, rfn, lock, -1);
+}
+EXPORT_SYMBOL(blk_init_allocated_queue);
+
+struct request_queue *
+blk_init_allocated_queue_node(struct request_queue *q, request_fn_proc *rfn,
+                              spinlock_t *lock, int node_id)
+{
         if (!q)
                 return NULL;
 
@@ -605,7 +621,7 @@ blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
         blk_put_queue(q);
         return NULL;
 }
-EXPORT_SYMBOL(blk_init_queue_node);
+EXPORT_SYMBOL(blk_init_allocated_queue_node);
 
 int blk_get_queue(struct request_queue *q)
 {
diff --git a/block/elevator.c b/block/elevator.c
index 5e734592bb40..6df2b5056b51 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -930,6 +930,7 @@ int elv_register_queue(struct request_queue *q)
         }
         return error;
 }
+EXPORT_SYMBOL(elv_register_queue);
 
 static void __elv_unregister_queue(struct elevator_queue *e)
 {
@@ -942,6 +943,7 @@ void elv_unregister_queue(struct request_queue *q)
         if (q)
                 __elv_unregister_queue(q->elevator);
 }
+EXPORT_SYMBOL(elv_unregister_queue);
 
 void elv_register(struct elevator_type *e)
 {