Re: [PATCH v4 1/8] media: virtio: Add protocol

[Brian Daniels <briandaniels@google.com>]

On Thu, Jun 25, 2026 at 8:51 PM Bryan O'Donoghue <bod@kernel.org> wrote:
>
> On 25/06/2026 21:24, Brian Daniels wrote:
> > I'm not an expert here, but taking a look at those files, the vast majority of
> > those reserved fields appear to be padding to ensure the struct has 64-bit
> > alignment, which matches the use here in virtio-media as well.
> >
> > virtio_pci appears to be the only device that explicitly states the
> > reserved bytes are for future extensions. Unless there's a good a reason to
> > expect a future use case where more space is needed, I would prefer to not add
> > more at this time.
>
> I'm querying why just the one though ? Why not say four ?
>
> Perhaps something you could address in your commit log.
>

Sure I can add a note in v5. But yeah the reason is the total struct
needs to be 64-bit aligned. So it can't be an arbitrary number.
And all the current reserved fields add the minimum number of bits to
ensure the existing structs are 64-bit aligned.
Adding more means extra bytes are transferred every exchange without
adding any value, which is inefficient.