block: add reference counting for struct bsg_job

Add reference counting to 'struct bsg_job' so we can implement a reuqest
timeout handler for bsg_jobs, which is needed for Fibre Channel.

Signed-off-by: Johannes Thumshirn <[e-mail]>
Reviewed-by: Hannes Reinecke <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

block/bsg-lib.c

···
  * bsg_destroy_job - routine to teardown/delete a bsg job
  * @job: bsg_job that is to be torn down
  */
-static void bsg_destroy_job(struct bsg_job *job)
+static void bsg_destroy_job(struct kref *kref)
 {
+	struct bsg_job *job = container_of(kref, struct bsg_job, kref);
+
 	put_device(job->dev);	/* release reference for the request */
 
 	kfree(job->request_payload.sg_list);
···
 	struct bsg_job *job = rq->special;
 
 	blk_end_request_all(rq, rq->errors);
-	bsg_destroy_job(job);
+	kref_put(&job->kref, bsg_destroy_job);
 }
 
 static int bsg_map_buffer(struct bsg_buffer *buf, struct request *req)
···
 	job->dev = dev;
 	/* take a reference for the request */
 	get_device(job->dev);
+	kref_init(&job->kref);
 	return 0;
 
 failjob_rls_rqst_payload:

include/linux/bsg-lib.h

···
 	struct device *dev;
 	struct request *req;
 
+	struct kref kref;
+
 	/* Transport/driver specific request/reply structs */
 	void *request;
 	void *reply;