drbd: prepare sending side for REQ_DISCARD

Note that I do NOT call __drbd_chk_io_error for failed REQ_DISCARD.
That may be wrong, though, or needs to differ between EOPNOTSUPP and
other errors...
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_main.c

@@ -1607,8 +1607,8 @@ static u32 bio_flags_to_wire(struct drbd_connection *connection, unsigned long b
 		return bi_rw & REQ_SYNC ? DP_RW_SYNC : 0;
 }
 
-/* Used to send write requests
- * R_PRIMARY -> Peer	(P_DATA)
+/* Used to send write or TRIM aka REQ_DISCARD requests
+ * R_PRIMARY -> Peer	(P_DATA, P_TRIM)
  */
 int drbd_send_dblock(struct drbd_peer_device *peer_device, struct drbd_request *req)
 {
@@ -1640,6 +1640,16 @@ int drbd_send_dblock(struct drbd_peer_device *peer_device, struct drbd_request *
 			dp_flags |= DP_SEND_WRITE_ACK;
 	}
 	p->dp_flags = cpu_to_be32(dp_flags);
+
+	if (dp_flags & DP_DISCARD) {
+		struct p_trim *t = (struct p_trim*)p;
+		t->size = cpu_to_be32(req->i.size);
+		err = __send_command(peer_device->connection, device->vnr, sock, P_TRIM, sizeof(*t), NULL, 0);
+		goto out;
+	}
+
+	/* our digest is still only over the payload.
+	 * TRIM does not carry any payload. */
 	if (dgs)
 		drbd_csum_bio(peer_device->connection->integrity_tfm, req->master_bio, p + 1);
 	err = __send_command(peer_device->connection, device->vnr, sock, P_DATA, sizeof(*p) + dgs, NULL, req->i.size);
@@ -1675,6 +1685,7 @@ int drbd_send_dblock(struct drbd_peer_device *peer_device, struct drbd_request *
 		     ... Be noisy about digest too large ...
 		} */
 	}
+out:
 	mutex_unlock(&sock->mutex);  /* locked by drbd_prepare_command() */
 
 	return err;

drivers/block/drbd/drbd_req.c

@@ -522,6 +522,13 @@ int __req_mod(struct drbd_request *req, enum drbd_req_event what,
 		mod_rq_state(req, m, RQ_LOCAL_PENDING, RQ_LOCAL_COMPLETED);
 		break;
 
+	case DISCARD_COMPLETED_NOTSUPP:
+	case DISCARD_COMPLETED_WITH_ERROR:
+		/* I'd rather not detach from local disk just because it
+		 * failed a REQ_DISCARD. */
+		mod_rq_state(req, m, RQ_LOCAL_PENDING, RQ_LOCAL_COMPLETED);
+		break;
+
 	case QUEUE_FOR_NET_READ:
 		/* READ or READA, and
 		 * no local disk,

drivers/block/drbd/drbd_req.h

@@ -110,11 +110,14 @@ enum drbd_req_event {
 	BARRIER_ACKED, /* in protocol A and B */
 	DATA_RECEIVED, /* (remote read) */
 
+	COMPLETED_OK,
 	READ_COMPLETED_WITH_ERROR,
 	READ_AHEAD_COMPLETED_WITH_ERROR,
 	WRITE_COMPLETED_WITH_ERROR,
+	DISCARD_COMPLETED_NOTSUPP,
+	DISCARD_COMPLETED_WITH_ERROR,
+
 	ABORT_DISK_IO,
-	COMPLETED_OK,
 	RESEND,
 	FAIL_FROZEN_DISK_IO,
 	RESTART_FROZEN_DISK_IO,

drivers/block/drbd/drbd_worker.c

@@ -267,7 +267,12 @@ void drbd_request_endio(struct bio *bio, int error)
 
 	/* to avoid recursion in __req_mod */
 	if (unlikely(error)) {
-		what = (bio_data_dir(bio) == WRITE)
+		if (bio->bi_rw & REQ_DISCARD)
+			what = (error == -EOPNOTSUPP)
+				? DISCARD_COMPLETED_NOTSUPP
+				: DISCARD_COMPLETED_WITH_ERROR;
+		else
+			what = (bio_data_dir(bio) == WRITE)
 			? WRITE_COMPLETED_WITH_ERROR
 			: (bio_rw(bio) == READ)
 			  ? READ_COMPLETED_WITH_ERROR