Re: [PATCH v4 07/12] block: reject zone appends that are not a multiple of the sector size

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Sep 07, 2026 at 01:07:42PM +0200, 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.
> 
> Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> ---
>  block/io.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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