drbd: zero-out partial unaligned discards on local backend

For consistency, also zero-out partial unaligned chunks of discard
requests on the local backend.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/drbd/drbd_int.h

@@ -1553,6 +1553,8 @@ extern void start_resync_timer_fn(unsigned long data);
 extern void drbd_endio_write_sec_final(struct drbd_peer_request *peer_req);
 
 /* drbd_receiver.c */
+extern int drbd_issue_discard_or_zero_out(struct drbd_device *device,
+		sector_t start, unsigned int nr_sectors, bool discard);
 extern int drbd_receiver(struct drbd_thread *thi);
 extern int drbd_ack_receiver(struct drbd_thread *thi);
 extern void drbd_send_ping_wf(struct work_struct *ws);

drivers/block/drbd/drbd_req.c

@@ -1156,6 +1156,16 @@ static int drbd_process_write_request(struct drbd_request *req)
 	return remote;
 }
 
+static void drbd_process_discard_req(struct drbd_request *req)
+{
+	int err = drbd_issue_discard_or_zero_out(req->device,
+				req->i.sector, req->i.size >> 9, true);
+
+	if (err)
+		req->private_bio->bi_error = -EIO;
+	bio_endio(req->private_bio);
+}
+
 static void
 drbd_submit_req_private_bio(struct drbd_request *req)
 {
@@ -1176,6 +1186,8 @@ drbd_submit_req_private_bio(struct drbd_request *req)
 				    : rw == READ  ? DRBD_FAULT_DT_RD
 				    :               DRBD_FAULT_DT_RA))
 			bio_io_error(bio);
+		else if (bio_op(bio) == REQ_OP_DISCARD)
+			drbd_process_discard_req(req);
 		else
 			generic_make_request(bio);
 		put_ldev(device);
@@ -1227,18 +1239,23 @@ drbd_request_prepare(struct drbd_device *device, struct bio *bio, unsigned long
 	/* Update disk stats */
 	_drbd_start_io_acct(device, req);
 
+	/* process discards always from our submitter thread */
+	if (bio_op(bio) & REQ_OP_DISCARD)
+		goto queue_for_submitter_thread;
+
 	if (rw == WRITE && req->private_bio && req->i.size
 	&& !test_bit(AL_SUSPENDED, &device->flags)) {
-		if (!drbd_al_begin_io_fastpath(device, &req->i)) {
-			atomic_inc(&device->ap_actlog_cnt);
-			drbd_queue_write(device, req);
-			return NULL;
-		}
+		if (!drbd_al_begin_io_fastpath(device, &req->i))
+			goto queue_for_submitter_thread;
 		req->rq_state |= RQ_IN_ACT_LOG;
 		req->in_actlog_jif = jiffies;
 	}
-
 	return req;
+
+ queue_for_submitter_thread:
+	atomic_inc(&device->ap_actlog_cnt);
+	drbd_queue_write(device, req);
+	return NULL;
 }
 
 static void drbd_send_and_submit(struct drbd_device *device, struct drbd_request *req)