nbd: use the correct block_device in nbd_bdev_reset

The bdev parameter to ->ioctl contains the block device that the ioctl
is called on, which can be the partition.  But the openers check in
nbd_bdev_reset really needs to check use the whole device, so switch to
using that.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220330052917.2566582-2-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/nbd.c

@@ -1217,11 +1217,11 @@ static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
 	return -ENOSPC;
 }
 
-static void nbd_bdev_reset(struct block_device *bdev)
+static void nbd_bdev_reset(struct nbd_device *nbd)
 {
-	if (bdev->bd_openers > 1)
+	if (nbd->disk->part0->bd_openers > 1)
 		return;
-	set_capacity(bdev->bd_disk, 0);
+	set_capacity(nbd->disk, 0);
 }
 
 static void nbd_parse_flags(struct nbd_device *nbd)
@@ -1386,7 +1386,7 @@ static int nbd_start_device(struct nbd_device *nbd)
 	return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
 }
 
-static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *bdev)
+static int nbd_start_device_ioctl(struct nbd_device *nbd)
 {
 	struct nbd_config *config = nbd->config;
 	int ret;
@@ -1405,7 +1405,7 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *b
 	flush_workqueue(nbd->recv_workq);
 
 	mutex_lock(&nbd->config_lock);
-	nbd_bdev_reset(bdev);
+	nbd_bdev_reset(nbd);
 	/* user requested, ignore socket errors */
 	if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags))
 		ret = 0;
@@ -1419,7 +1419,7 @@ static void nbd_clear_sock_ioctl(struct nbd_device *nbd,
 {
 	sock_shutdown(nbd);
 	__invalidate_device(bdev, true);
-	nbd_bdev_reset(bdev);
+	nbd_bdev_reset(nbd);
 	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
 			       &nbd->config->runtime_flags))
 		nbd_config_put(nbd);
@@ -1465,7 +1465,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		config->flags = arg;
 		return 0;
 	case NBD_DO_IT:
-		return nbd_start_device_ioctl(nbd, bdev);
+		return nbd_start_device_ioctl(nbd);
 	case NBD_CLEAR_QUE:
 		/*
 		 * This is for compatibility only.  The queue is always cleared