drbd: Create the protocol feature THIN_RESYNC

If thinly provisioned volumes are used, during a resync the sync source
tries to find out if a block is deallocated. If it is deallocated, then
the resync target uses block_dev_issue_zeroout() on the range in
question.
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_protocol.h

@@ -165,6 +165,7 @@ struct p_block_req {
  */
 
 #define FF_TRIM      1
+#define FF_THIN_RESYNC 2
 
 struct p_connection_features {
 	u32 protocol_min;

drivers/block/drbd/drbd_receiver.c

@@ -48,7 +48,7 @@
 #include "drbd_req.h"
 #include "drbd_vli.h"
 
-#define PRO_FEATURES (FF_TRIM)
+#define PRO_FEATURES (FF_TRIM | FF_THIN_RESYNC)
 
 struct packet_info {
 	enum drbd_packet cmd;
@@ -4991,6 +4991,9 @@ static int drbd_do_features(struct drbd_connection *connection)
 	drbd_info(connection, "Agreed to%ssupport TRIM on protocol level\n",
 		  connection->agreed_features & FF_TRIM ? " " : " not ");
 
+	drbd_info(connection, "Agreed to%ssupport THIN_RESYNC on protocol level\n",
+		  connection->agreed_features & FF_THIN_RESYNC ? " " : " not ");
+
 	return 1;
 
  incompat:

drivers/block/drbd/drbd_worker.c

@@ -583,6 +583,7 @@ static int make_resync_request(struct drbd_device *const device, int cancel)
 	int number, rollback_i, size;
 	int align, requeue = 0;
 	int i = 0;
+	int discard_granularity = 0;
 
 	if (unlikely(cancel))
 		return 0;
@@ -602,6 +603,12 @@ static int make_resync_request(struct drbd_device *const device, int cancel)
 		return 0;
 	}
 
+	if (connection->agreed_features & FF_THIN_RESYNC) {
+		rcu_read_lock();
+		discard_granularity = rcu_dereference(device->ldev->disk_conf)->rs_discard_granularity;
+		rcu_read_unlock();
+	}
+
 	max_bio_size = queue_max_hw_sectors(device->rq_queue) << 9;
 	number = drbd_rs_number_requests(device);
 	if (number <= 0)
@@ -666,6 +673,9 @@ static int make_resync_request(struct drbd_device *const device, int cancel)
 			if (sector & ((1<<(align+3))-1))
 				break;
 
+			if (discard_granularity && size == discard_granularity)
+				break;
+
 			/* do not cross extent boundaries */
 			if (((bit+1) & BM_BLOCKS_PER_BM_EXT_MASK) == 0)
 				break;
@@ -712,7 +722,8 @@ static int make_resync_request(struct drbd_device *const device, int cancel)
 			int err;
 
 			inc_rs_pending(device);
-			err = drbd_send_drequest(peer_device, P_RS_DATA_REQUEST,
+			err = drbd_send_drequest(peer_device,
+						 size == discard_granularity ? P_RS_THIN_REQ : P_RS_DATA_REQUEST,
 						 sector, size, ID_SYNCER);
 			if (err) {
 				drbd_err(device, "drbd_send_drequest() failed, aborting...\n");