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

[Damien Le Moal]

On 2021/04/19 18:29, 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.

This is only to avoid someone from running zoned-btrfs on top of dm-crypt.
Without this patch, mount will be OK and file data writes will also actually be
OK. But all reads will miserably fail... I would rather have this patch in than
deal with the "bug reports" about btrfs failing to read files. No ?

Note that like you, I dislike having to add such code. But it was my oversight
when I worked on getting dm-crypt to work on zoned drives. Zone append was
overlooked at that time... My bad, really.


-- 
Damien Le Moal
Western Digital Research