Re: [RFC PATCH v4 3/3] bcache: reject writeback cache mode for zoned backing device

[Coly Li <colyli@suse.de>]

On 2020/5/25 09:26, Damien Le Moal wrote:
> On 2020/05/22 21:19, Coly Li wrote:
>> 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>
>> Cc: Damien Le Moal <damien.lemoal@wdc.com>
>> Cc: Hannes Reinecke <hare@suse.com>
>> Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
>> ---
>>  drivers/md/bcache/sysfs.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
>> index 323276994aab..41bdbc42a17d 100644
>> --- a/drivers/md/bcache/sysfs.c
>> +++ b/drivers/md/bcache/sysfs.c
>> @@ -359,6 +359,11 @@ STORE(__cached_dev)
>>  		if (v < 0)
>>  			return v;
>>  
>> +		if ((unsigned int) v == CACHE_MODE_WRITEBACK) {
>> +			pr_err("writeback mode is not supported for zoned backing device.\n");
>> +			return -ENOTSUPP;
>> +		}
>> +
>>  		if ((unsigned int) v != BDEV_CACHE_MODE(&dc->sb)) {
>>  			SET_BDEV_CACHE_MODE(&dc->sb, v);
>>  			bch_write_bdev_super(dc, NULL);
>>
> 
> Do you have a similar check in bcache user tools at format time ? Or is the
> cache mode specified only when the bcache device is started ?

Yes I do the cache mode check in bcache-tools, and if user sets
writeback mode, bcache-tools will inform user and switch it to
writethrough mode explicitly.

> 
> Looks good.
> 
> Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
> 

Thank you for the review!

Coly Li