drbd: disambiguation, s/P_DISCARD_WRITE/P_SUPERSEDED/

To avoid confusion with REQ_DISCARD aka TRIM, rename our
"discard concurrent write acks" from P_DISCARD_WRITE to P_SUPERSEDED.

At the same time, rename the drbd request event DISCARD_WRITE
to CONFLICT_RESOLVED. It already triggers both successful completion
or restart of the request, depending on our RQ_POSTPONED flag.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_int.h

@@ -197,7 +197,7 @@ enum drbd_packet {
 	P_RECV_ACK	      = 0x15, /* Used in protocol B */
 	P_WRITE_ACK	      = 0x16, /* Used in protocol C */
 	P_RS_WRITE_ACK	      = 0x17, /* Is a P_WRITE_ACK, additionally call set_in_sync(). */
-	P_DISCARD_WRITE	      = 0x18, /* Used in proto C, two-primaries conflict detection */
+	P_SUPERSEDED	      = 0x18, /* Used in proto C, two-primaries conflict detection */
 	P_NEG_ACK	      = 0x19, /* Sent if local disk is unusable */
 	P_NEG_DREPLY	      = 0x1a, /* Local disk is broken... */
 	P_NEG_RS_DREPLY	      = 0x1b, /* Local disk is broken... */
@@ -335,7 +335,7 @@ struct p_data {
  * commands which share a struct:
  *  p_block_ack:
  *   P_RECV_ACK (proto B), P_WRITE_ACK (proto C),
- *   P_DISCARD_WRITE (proto C, two-primaries conflict detection)
+ *   P_SUPERSEDED (proto C, two-primaries conflict detection)
  *  p_block_req:
  *   P_DATA_REQUEST, P_RS_DATA_REQUEST
  */

drivers/block/drbd/drbd_main.c

@@ -3339,7 +3339,7 @@ const char *cmdname(enum drbd_packet cmd)
 		[P_RECV_ACK]	        = "RecvAck",
 		[P_WRITE_ACK]	        = "WriteAck",
 		[P_RS_WRITE_ACK]	= "RSWriteAck",
-		[P_DISCARD_WRITE]        = "DiscardWrite",
+		[P_SUPERSEDED]          = "Superseded",
 		[P_NEG_ACK]	        = "NegAck",
 		[P_NEG_DREPLY]	        = "NegDReply",
 		[P_NEG_RS_DREPLY]	= "NegRSDReply",

drivers/block/drbd/drbd_receiver.c

@@ -425,7 +425,7 @@ static int drbd_finish_peer_reqs(struct drbd_conf *mdev)
 		drbd_free_net_peer_req(mdev, peer_req);
 
 	/* possible callbacks here:
-	 * e_end_block, and e_end_resync_block, e_send_discard_write.
+	 * e_end_block, and e_end_resync_block, e_send_superseded.
 	 * all ignore the last argument.
 	 */
 	list_for_each_entry_safe(peer_req, t, &work_list, w.list) {
@@ -1803,7 +1803,7 @@ static void restart_conflicting_writes(struct drbd_conf *mdev,
 			continue;
 		/* as it is RQ_POSTPONED, this will cause it to
 		 * be queued on the retry workqueue. */
-		__req_mod(req, DISCARD_WRITE, NULL);
+		__req_mod(req, CONFLICT_RESOLVED, NULL);
 	}
 }
 
@@ -1864,17 +1864,17 @@ static int e_send_ack(struct drbd_work *w, enum drbd_packet ack)
 	return err;
 }
 
-static int e_send_discard_write(struct drbd_work *w, int unused)
+static int e_send_superseded(struct drbd_work *w, int unused)
 {
-	return e_send_ack(w, P_DISCARD_WRITE);
+	return e_send_ack(w, P_SUPERSEDED);
 }
 
 static int e_send_retry_write(struct drbd_work *w, int unused)
 {
 	struct drbd_tconn *tconn = w->mdev->tconn;
 
 	return e_send_ack(w, tconn->agreed_pro_version >= 100 ?
-			     P_RETRY_WRITE : P_DISCARD_WRITE);
+			     P_RETRY_WRITE : P_SUPERSEDED);
 }
 
 static bool seq_greater(u32 a, u32 b)
@@ -2082,11 +2082,11 @@ static int handle_write_conflicts(struct drbd_conf *mdev,
 		if (resolve_conflicts) {
 			/*
 			 * If the peer request is fully contained within the
-			 * overlapping request, it can be discarded; otherwise,
-			 * it will be retried once all overlapping requests
-			 * have completed.
+			 * overlapping request, it can be considered overwritten
+			 * and thus superseded; otherwise, it will be retried
+			 * once all overlapping requests have completed.
 			 */
-			bool discard = i->sector <= sector && i->sector +
+			bool superseded = i->sector <= sector && i->sector +
 				       (i->size >> 9) >= sector + (size >> 9);
 
 			if (!equal)
@@ -2095,10 +2095,10 @@ static int handle_write_conflicts(struct drbd_conf *mdev,
 					       "assuming %s came first\n",
 					  (unsigned long long)i->sector, i->size,
 					  (unsigned long long)sector, size,
-					  discard ? "local" : "remote");
+					  superseded ? "local" : "remote");
 
 			inc_unacked(mdev);
-			peer_req->w.cb = discard ? e_send_discard_write :
+			peer_req->w.cb = superseded ? e_send_superseded :
 						   e_send_retry_write;
 			list_add_tail(&peer_req->w.list, &mdev->done_ee);
 			wake_asender(mdev->tconn);
@@ -2119,8 +2119,9 @@ static int handle_write_conflicts(struct drbd_conf *mdev,
 			    !(req->rq_state & RQ_POSTPONED)) {
 				/*
 				 * Wait for the node with the discard flag to
-				 * decide if this request will be discarded or
-				 * retried.  Requests that are discarded will
+				 * decide if this request has been superseded
+				 * or needs to be retried.
+				 * Requests that have been superseded will
 				 * disappear from the write_requests tree.
 				 *
 				 * In addition, wait for the conflicting
@@ -4994,8 +4995,8 @@ static int got_BlockAck(struct drbd_tconn *tconn, struct packet_info *pi)
 	case P_RECV_ACK:
 		what = RECV_ACKED_BY_PEER;
 		break;
-	case P_DISCARD_WRITE:
-		what = DISCARD_WRITE;
+	case P_SUPERSEDED:
+		what = CONFLICT_RESOLVED;
 		break;
 	case P_RETRY_WRITE:
 		what = POSTPONE_WRITE;
@@ -5220,7 +5221,7 @@ static struct asender_cmd asender_tbl[] = {
 	[P_RECV_ACK]	    = { sizeof(struct p_block_ack), got_BlockAck },
 	[P_WRITE_ACK]	    = { sizeof(struct p_block_ack), got_BlockAck },
 	[P_RS_WRITE_ACK]    = { sizeof(struct p_block_ack), got_BlockAck },
-	[P_DISCARD_WRITE]   = { sizeof(struct p_block_ack), got_BlockAck },
+	[P_SUPERSEDED]   = { sizeof(struct p_block_ack), got_BlockAck },
 	[P_NEG_ACK]	    = { sizeof(struct p_block_ack), got_NegAck },
 	[P_NEG_DREPLY]	    = { sizeof(struct p_block_ack), got_NegDReply },
 	[P_NEG_RS_DREPLY]   = { sizeof(struct p_block_ack), got_NegRSDReply },

drivers/block/drbd/drbd_req.c

@@ -611,13 +611,13 @@ int __req_mod(struct drbd_request *req, enum drbd_req_event what,
 				RQ_NET_DONE);
 		break;
 
-	case DISCARD_WRITE:
-		/* for discarded conflicting writes of multiple primaries,
+	case CONFLICT_RESOLVED:
+		/* for superseded conflicting writes of multiple primaries,
 		 * there is no need to keep anything in the tl, potential
 		 * node crashes are covered by the activity log.
 		 *
 		 * If this request had been marked as RQ_POSTPONED before,
-		 * it will actually not be discarded, but "restarted",
+		 * it will actually not be completed, but "restarted",
 		 * resubmitted from the retry worker context. */
 		D_ASSERT(req->rq_state & RQ_NET_PENDING);
 		D_ASSERT(req->rq_state & RQ_EXP_WRITE_ACK);

drivers/block/drbd/drbd_req.h

@@ -97,7 +97,7 @@ enum drbd_req_event {
 	RECV_ACKED_BY_PEER,
 	WRITE_ACKED_BY_PEER,
 	WRITE_ACKED_BY_PEER_AND_SIS, /* and set_in_sync */
-	DISCARD_WRITE,
+	CONFLICT_RESOLVED,
 	POSTPONE_WRITE,
 	NEG_ACKED,
 	BARRIER_ACKED, /* in protocol A and B */