[PATCH 3/4] btrfs: zoned: fail mount if the device does not support zone append

[Johannes Thumshirn]

On 19/04/2021 11:29, Christoph Hellwig wrote:
> On Fri, Apr 16, 2021 at 06:17:21PM +0200, David Sterba wrote:
>> On Fri, Apr 16, 2021 at 12:05:27PM +0900, Damien Le Moal wrote:
>>> From: Johannes Thumshirn <johannes.thumshirn at wdc.com>
>>>
>>> For zoned btrfs, zone append is mandatory to write to a sequential write
>>> only zone, otherwise parallel writes to the same zone could result in
>>> unaligned write errors.
>>>
>>> If a zoned block device does not support zone append (e.g. a dm-crypt
>>> zoned device using a non-NULL IV cypher), fail to mount.
>>>
>>> Signed-off-by: Johannes Thumshirn <johannes.thumshirn at wdc.com>
>>> Signed-off-by: Damien Le Moal <damien.lemoal at wdc.com>
>>
>> Added to misc-next, thanks. I'll queue it for 5.13, it's not an urgent
>> fix for 5.12 release but i'll tag it as stable so it'll apear in 5.12.x
>> later.
> 
> Please don't.  Zone append is a strict requirement for zoned devices,
> no need to add cargo cult code like this everywhere.
> 

As of now, dm-crypt supports zoned devices but cannot really work with 
zone append. At least not with ciphers that use sectors as IV.
OTOH btrfs cannot work without zone append. While we won't notice any 
problems with writes, reads (or better decrypt) will fail.