Re: [PATCH 10/12] virtio-blk: derive the maximum zone append size

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

On 8/26/26 05:57, Niklas Cassel wrote:
> The max_append_sectors field of virtio_blk_zoned_characteristics must be
> set by the device to the largest zone append request that can be issued
> to it, and a value of zero tells the guest driver that zone append is not
> supported at all (virtio 1.4, 5.2.5.2). Linux refuses to attach a zoned
> device that reports zero.
> 
> We pass BlockLimits.max_append_sectors straight through, which makes that
> field mean "zone append unsupported" when it is unset, rather than "this
> backend imposes no limit of its own". Only a backend that has a limit of
> its own has anything to put there.
> 
> Derive the value instead. A backend limit is honoured when there is one,
> and otherwise the request is bounded by the zone size, since an append
> cannot cross a zone boundary, and by the largest request the block layer
> can carry. The result cannot be zero.
> 
> A backend that carries out an append itself, rather than passing it to a
> device that has a limit of its own, is the one that knows how large a
> request its implementation can take, so it reports that in
> BlockLimits.max_append_sectors and this does not have to guess at it.
> 
> Signed-off-by: Niklas Cassel <cassel@kernel.org>

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

-- 
Damien Le Moal
Western Digital Research