Re: [virtio-comment] [PATCH] virtio-vsock: add max payload size config field

[Laura Loghin <lauralg@amazon.com>]

On 6/15/22 17:11, Stefan Hajnoczi wrote:

> On Mon, Apr 04, 2022 at 04:49:31PM +0300, Laura Loghin wrote:
> > @@ -57,6 +62,35 @@ \subsection{Device configuration layout}\label{sec:Device Types / Socket Device
> >  \hline
> >  \end{tabular}
> >  
> > +The following driver-read-only field, \field{data_max_size} only exists if
> > +VIRTIO_VSOCK_F_SIZE_MAX is set. This field specifies the maximum packet payload
> > +size for the driver to use.
> >       
> This wording can be misinterpreted but can be kept for now. This wording
> should be updated when the next field is added in the future, indicating
> that the field is only *used* when VIRTIO_VSOCK_F_SIZE_MAX has been
> negotiated. Further fields will be located after data_max_size so the
> field certainly *exists* even when VIRTIO_VSOCK_F_SIZE_MAX is not set.
>
> If someone misinterprets this they might think the config struct layout
> depends on the combination of negotiated feature bits. That's not the
> case, the layout is always the same. The size of the struct depends on
> the features offered by the device.
>
> Similar wording is used elsewhere in the spec, so we may want to clarify
> it for the entire spec.
>
> Stefan
>     
Yes, I agree with you. In fact when I added this section I had a look at
the corresponding ones from other devices, and got confused by the wording.
My understanding actually was that the field won't exist, but indeed I
found it pretty weird, so it would be great if we can update all the spec
sections that are propagating this misinterpretation. For now, I will
update the section in this patch.

Thanks,
Laura

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