block: implement an unprep function corresponding directly to prep

Reviewed-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

block/blk-core.c

@@ -608,6 +608,7 @@ blk_init_allocated_queue_node(struct request_queue *q, request_fn_proc *rfn,
 
 	q->request_fn		= rfn;
 	q->prep_rq_fn		= NULL;
+	q->unprep_rq_fn		= NULL;
 	q->unplug_fn		= generic_unplug_device;
 	q->queue_flags		= QUEUE_FLAG_DEFAULT;
 	q->queue_lock		= lock;
@@ -2133,6 +2134,26 @@ static bool blk_update_bidi_request(struct request *rq, int error,
 	return false;
 }
 
+/**
+ * blk_unprep_request - unprepare a request
+ * @req:	the request
+ *
+ * This function makes a request ready for complete resubmission (or
+ * completion).  It happens only after all error handling is complete,
+ * so represents the appropriate moment to deallocate any resources
+ * that were allocated to the request in the prep_rq_fn.  The queue
+ * lock is held when calling this.
+ */
+void blk_unprep_request(struct request *req)
+{
+	struct request_queue *q = req->q;
+
+	req->cmd_flags &= ~REQ_DONTPREP;
+	if (q->unprep_rq_fn)
+		q->unprep_rq_fn(q, req);
+}
+EXPORT_SYMBOL_GPL(blk_unprep_request);
+
 /*
  * queue lock must be held
  */
@@ -2148,6 +2169,10 @@ static void blk_finish_request(struct request *req, int error)
 
 	blk_delete_timer(req);
 
+	if (req->cmd_flags & REQ_DONTPREP)
+		blk_unprep_request(req);
+
+
 	blk_account_io_done(req);
 
 	if (req->end_io)

block/blk-settings.c

@@ -36,6 +36,23 @@ void blk_queue_prep_rq(struct request_queue *q, prep_rq_fn *pfn)
 }
 EXPORT_SYMBOL(blk_queue_prep_rq);
 
+/**
+ * blk_queue_unprep_rq - set an unprepare_request function for queue
+ * @q:		queue
+ * @ufn:	unprepare_request function
+ *
+ * It's possible for a queue to register an unprepare_request callback
+ * which is invoked before the request is finally completed. The goal
+ * of the function is to deallocate any data that was allocated in the
+ * prepare_request callback.
+ *
+ */
+void blk_queue_unprep_rq(struct request_queue *q, unprep_rq_fn *ufn)
+{
+	q->unprep_rq_fn = ufn;
+}
+EXPORT_SYMBOL(blk_queue_unprep_rq);
+
 /**
  * blk_queue_merge_bvec - set a merge_bvec function for queue
  * @q:		queue

drivers/scsi/scsi_lib.c

@@ -85,7 +85,7 @@ static void scsi_unprep_request(struct request *req)
 {
 	struct scsi_cmnd *cmd = req->special;
 
-	req->cmd_flags &= ~REQ_DONTPREP;
+	blk_unprep_request(req);
 	req->special = NULL;
 
 	scsi_put_command(cmd);

include/linux/blkdev.h

@@ -200,6 +200,7 @@ struct request_pm_state
 typedef void (request_fn_proc) (struct request_queue *q);
 typedef int (make_request_fn) (struct request_queue *q, struct bio *bio);
 typedef int (prep_rq_fn) (struct request_queue *, struct request *);
+typedef void (unprep_rq_fn) (struct request_queue *, struct request *);
 typedef void (unplug_fn) (struct request_queue *);
 
 struct bio_vec;
@@ -282,6 +283,7 @@ struct request_queue
 	request_fn_proc		*request_fn;
 	make_request_fn		*make_request_fn;
 	prep_rq_fn		*prep_rq_fn;
+	unprep_rq_fn		*unprep_rq_fn;
 	unplug_fn		*unplug_fn;
 	merge_bvec_fn		*merge_bvec_fn;
 	prepare_flush_fn	*prepare_flush_fn;
@@ -841,6 +843,7 @@ extern void blk_complete_request(struct request *);
 extern void __blk_complete_request(struct request *);
 extern void blk_abort_request(struct request *);
 extern void blk_abort_queue(struct request_queue *);
+extern void blk_unprep_request(struct request *);
 
 /*
  * Access functions for manipulating queue properties
@@ -885,6 +888,7 @@ extern int blk_queue_dma_drain(struct request_queue *q,
 extern void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn);
 extern void blk_queue_segment_boundary(struct request_queue *, unsigned long);
 extern void blk_queue_prep_rq(struct request_queue *, prep_rq_fn *pfn);
+extern void blk_queue_unprep_rq(struct request_queue *, unprep_rq_fn *ufn);
 extern void blk_queue_merge_bvec(struct request_queue *, merge_bvec_fn *);
 extern void blk_queue_dma_alignment(struct request_queue *, int);
 extern void blk_queue_update_dma_alignment(struct request_queue *, int);