drbd: split out a drbd_discard_supported helper

Add a helper to check if discard is supported for a given connection /
backing device combination.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Philipp Reisner <philipp.reisner@linbit.com>
Reviewed-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Tested-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Link: https://lore.kernel.org/r/20240306140332.623759-7-philipp.reisner@linbit.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/drbd/drbd_nl.c

@@ -1231,24 +1231,33 @@ static unsigned int drbd_max_discard_sectors(struct drbd_connection *connection)
 	return AL_EXTENT_SIZE >> 9;
 }
 
-static void decide_on_discard_support(struct drbd_device *device,
+static bool drbd_discard_supported(struct drbd_connection *connection,
 		struct drbd_backing_dev *bdev)
 {
-	struct drbd_connection *connection =
-		first_peer_device(device)->connection;
-	struct request_queue *q = device->rq_queue;
-	unsigned int max_discard_sectors;
-
 	if (bdev && !bdev_max_discard_sectors(bdev->backing_bdev))
-		goto not_supported;
+		return false;
 
 	if (connection->cstate >= C_CONNECTED &&
 	    !(connection->agreed_features & DRBD_FF_TRIM)) {
 		drbd_info(connection,
 			"peer DRBD too old, does not support TRIM: disabling discards\n");
-		goto not_supported;
+		return false;
 	}
 
+	return true;
+}
+
+static void decide_on_discard_support(struct drbd_device *device,
+		struct drbd_backing_dev *bdev)
+{
+	struct drbd_connection *connection =
+		first_peer_device(device)->connection;
+	struct request_queue *q = device->rq_queue;
+	unsigned int max_discard_sectors;
+
+	if (!drbd_discard_supported(connection, bdev))
+		goto not_supported;
+
 	/*
 	 * We don't care for the granularity, really.
 	 *