bcache: reject writeback cache mode for zoned backing device

Currently we don't support writeback mode for zoned device as backing
device. So reject it by sysfs interface.

This rejection will be removed after the writeback cache mode support
for zoned device gets done.

Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
1 file changed