btrfs: don't allow adding block device of less than 1 MB

Commit 15ae0410c37a79 ("btrfs-progs: add error handling for
device_get_partition_size_fd_stat()") in btrfs-progs inadvertently
changed it so that if the BLKGETSIZE64 ioctl on a block device returned
a size of 0, this was no longer seen as an error condition.

Unfortunately this is how disconnected NBD devices behave, meaning that
with btrfs-progs 6.16 it's now possible to add a device you can't
remove:

  # btrfs device add /dev/nbd0 /root/temp
  # btrfs device remove /dev/nbd0 /root/temp
  ERROR: error removing device '/dev/nbd0': Invalid argument

This check should always have been done kernel-side anyway, so add a
check in btrfs_init_new_device() that the new device doesn't have a size
less than BTRFS_DEVICE_RANGE_RESERVED (i.e. 1 MB).

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Mark Harmstone <mark@harmstone.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: maharmstone

fs/btrfs/volumes.c

@@ -2722,6 +2722,11 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 		goto error;
 	}
 
+	if (bdev_nr_bytes(file_bdev(bdev_file)) <= BTRFS_DEVICE_RANGE_RESERVED) {
+		ret = -EINVAL;
+		goto error;
+	}
+
 	if (fs_devices->seeding) {
 		seeding_dev = true;
 		down_write(&sb->s_umount);