Re: [PATCH 07/12] block: reject zone appends that are not a multiple of the sector size

[Damien Le Moal <dlemoal@kernel.org>]

On 8/26/26 05:57, Niklas Cassel wrote:
> Zone write pointers are tracked and reported in units of
> BDRV_SECTOR_SIZE, so an append whose data size is not a multiple of it
> would leave a write pointer that cannot be represented, neither in a
> BlockZoneDescriptor nor in the virtio and NVMe zone reports derived from
> one.
> 
> Nothing states that invariant. file-posix, the only driver that carries
> out an append itself, does enforce it, but only as a side effect of
> checking each iovec against BlockLimits.write_granularity, which is never
> smaller than the sector size. That conflates two constraints: the sector
> granularity holds for every driver, whereas write_granularity describes a
> coarser requirement of the medium below a driver, and only a driver that
> has such a medium should express it.
> 
> Check the invariant once in bdrv_co_zone_append(), so that it no longer
> rests on a driver that happens to have a granularity of its own to
> report.
> 
> This is a lower bound, not the alignment that a guest has to observe. The
> block layer cannot know that one, because it also depends on the logical
> block size the device is configured with, which is a property of the
> frontend. The alignment that applies to a guest is the larger of the two,
> and it is the frontend that reports it, that validates requests against
> it, and that has to refuse a device whose write pointers do not satisfy
> it.
> 
> Signed-off-by: Niklas Cassel <cassel@kernel.org>

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>


-- 
Damien Le Moal
Western Digital Research