blk-mq: add ->init_request and ->exit_request methods

The current blk_mq_init_commands/blk_mq_free_commands interface has a
two problems:

 1) Because only the constructor is passed to blk_mq_init_commands there
    is no easy way to clean up when a comman initialization failed.  The
    current code simply leaks the allocations done in the constructor.

 2) There is no good place to call blk_mq_free_commands: before
    blk_cleanup_queue there is no guarantee that all outstanding
    commands have completed, so we can't free them yet.  After
    blk_cleanup_queue the queue has usually been freed.  This can be
    worked around by grabbing an unconditional reference before calling
    blk_cleanup_queue and dropping it after blk_mq_free_commands is
    done, although that's not exatly pretty and driver writers are
    guaranteed to get it wrong sooner or later.

Both issues are easily fixed by making the request constructor and
destructor normal blk_mq_ops methods.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index b6ee48740458..29c1a6e83814 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -67,6 +67,10 @@ typedef struct blk_mq_hw_ctx *(alloc_hctx_fn)(struct blk_mq_reg *,unsigned int);
 typedef void (free_hctx_fn)(struct blk_mq_hw_ctx *, unsigned int);
 typedef int (init_hctx_fn)(struct blk_mq_hw_ctx *, void *, unsigned int);
 typedef void (exit_hctx_fn)(struct blk_mq_hw_ctx *, unsigned int);
+typedef int (init_request_fn)(void *, struct blk_mq_hw_ctx *,
+                struct request *, unsigned int);
+typedef void (exit_request_fn)(void *, struct blk_mq_hw_ctx *,
+                struct request *, unsigned int);
 
 struct blk_mq_ops {
         /*
@@ -99,6 +103,14 @@ struct blk_mq_ops {
          */
         init_hctx_fn            *init_hctx;
         exit_hctx_fn            *exit_hctx;
+
+        /*
+         * Called for every command allocated by the block layer to allow
+         * the driver to set up driver specific data.
+         * Ditto for exit/teardown.
+         */
+        init_request_fn         *init_request;
+        exit_request_fn         *exit_request;
 };
 
 enum {
@@ -118,8 +130,6 @@ enum {
 struct request_queue *blk_mq_init_queue(struct blk_mq_reg *, void *);
 int blk_mq_register_disk(struct gendisk *);
 void blk_mq_unregister_disk(struct gendisk *);
-int blk_mq_init_commands(struct request_queue *, int (*init)(void *data, struct blk_mq_hw_ctx *, struct request *, unsigned int), void *data);
-void blk_mq_free_commands(struct request_queue *, void (*free)(void *data, struct blk_mq_hw_ctx *, struct request *, unsigned int), void *data);
 
 void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule);