RE: [virtio-comment] Re: [PATCH v2 1/2] virtio-net: Fix receive buffer size calculation text

[Cornelia Huck <cohuck@redhat.com>]

On Mon, Feb 05 2024, Parav Pandit <parav@nvidia.com> wrote:

>> From: Cornelia Huck <cohuck@redhat.com>
>> Sent: Monday, February 5, 2024 8:50 PM
>> 
>> On Tue, Jan 16 2024, "Michael S. Tsirkin" <mst@redhat.com> wrote:
>> 
>> > On Tue, Jan 16, 2024 at 01:18:59PM +0000, Parav Pandit wrote:
>> >>
>> >> > From: Cornelia Huck <cohuck@redhat.com>
>> >> > Sent: Tuesday, January 16, 2024 6:08 PM
>> >> > To: Parav Pandit <parav@nvidia.com>;
>> >> > virtio-comment@lists.oasis-open.org;
>> >> > mst@redhat.com
>> >> > Cc: Shahaf Shuler <shahafs@nvidia.com>; xuanzhuo@linux.alibaba.com;
>> >> > yuri.benditovich@daynix.com
>> >> > Subject: RE: [PATCH v2 1/2] virtio-net: Fix receive buffer size
>> >> > calculation text
>> >> >
>> >> > On Tue, Jan 16 2024, Parav Pandit <parav@nvidia.com> wrote:
>> >> >
>> >> > >> From: Cornelia Huck <cohuck@redhat.com>
>> >> > >> Sent: Tuesday, January 16, 2024 4:33 PM
>> >> > >> To: Parav Pandit <parav@nvidia.com>;
>> >> > >> virtio-comment@lists.oasis-open.org;
>> >> > >> mst@redhat.com
>> >> > >> Cc: Shahaf Shuler <shahafs@nvidia.com>;
>> >> > >> xuanzhuo@linux.alibaba.com; yuri.benditovich@daynix.com
>> >> > >> Subject: RE: [PATCH v2 1/2] virtio-net: Fix receive buffer size
>> >> > >> calculation text
>> >> > >>
>> >> > >> On Tue, Jan 16 2024, Parav Pandit <parav@nvidia.com> wrote:
>> >> > >>
>> >> > >> >> From: Cornelia Huck <cohuck@redhat.com>
>> >> > >> >> Sent: Monday, January 15, 2024 10:14 PM
>> >> > >> >
>> >> > >> >> On Mon, Jan 15 2024, Parav Pandit <parav@nvidia.com> wrote:
>> >> > >> >> > +The driver MUST consider size of field \field{struct
>> >> > >> >> > +virtio_net_hdr}
>> >> > >> >> > +20 bytes if VIRTIO_NET_F_HASH_REPORT is negotiated, and 12
>> >> > >> >> > +bytes if
>> >> > >> >> not.
>> >> > >> >> > +
>> >> > >> >>
>> >> > >> >> Requiring the driver to consider the size of something to be
>> >> > >> >> its actual size seems a bit odd :) I don't think we need
>> >> > >> >> this, as the
>> 
>> My comment here still holds.
>>
> It is a variable length data structure with few trailing fields as not valid.
> The "actual size" depends on negotiated feature bit, which is what is written here.
>  
> How about below?
>
> When calculating the size of \field{struct virtio_net_hdr}, the driver must consider all the fields
> inclusive up to \field{padding_reserved}, i.e. 20 bytes if VIRTIO_NET_F_HASH_REPORT is negotiated,
> and 12 bytes if not.

It's up to padding_reserved with F_HASH_REPORT and up to num_buffers if
not, isn't it?