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Subject: Re: [virtio-comment] [PATCH v4] virtio-vsock: add max payload size config field
On Thu, Jun 16 2022, "Michael S. Tsirkin" <mst@redhat.com> wrote: > On Tue, Jun 14, 2022 at 01:57:34PM +0200, Halil Pasic wrote: >> On Mon, 13 Jun 2022 13:40:38 +0300 >> Laura Loghin <lauralg@amazon.com> wrote: >> >> > @@ -57,6 +62,25 @@ \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. >> > + >> > +\devicenormative{\subsubsection}{Device configuration layout}{Device Types / Socket Device / Device configuration layout} >> > + >> > +The device MUST NOT change the value exposed through \field{data_max_size}. >> > + >> > +\drivernormative{\subsubsection}{Device configuration layout}{Device Types / Socket Device / Device configuration layout} >> > + >> > +A driver SHOULD negotiate VIRTIO_VSOCK_F_SIZE_MAX if the device offers it. >> > + >> > +If the driver negotiates VIRTIO_VSOCK_F_SIZE_MAX, the receive buffers it >> > +supplies for a packet MUST have a total size that doesn't exceed the size >> > +\field{data_max_size} (plus header length). >> > + >> > +If the driver negotiates VIRTIO_VSOCK_F_SIZE_MAX, it MUST NOT transmit packets >> > +of size exceeding the value of \field{data_max_size} (plus header length). >> > + >> >> Hi and sorry for being late to the party! >> >> I believe I do understand why do we want to put a restriction on the >> size of the transmitted packets, but I would appreciate if you could >> explain to me why do we want to limit the receive buffer size. >> >> Also I find the wording regarding a little bit ambiguous because >> in a networking context it also makes sense to talk about the size of the >> receive buffer. I guess hear we are talking about a single virtio buffer >> (a descriptor chain described potentially non-continuous (or compact in >> the mathematical sense of the word) which is composed from as many >> continuous chunks of memory as many descriptors are contained within the >> descriptor chain). If we are indeed talking about a single virtio buffer, >> I don't understand the plural. If not, I'm not sure what are we talking >> about. > > I think I agree here, I don't understand the mix of "buffers" and "a > packet" either. > > I voted "no" on the ballot, though if others feel we should apply as > is and fix up later, that is not too bad. I now switched to "no" as well; it's not too bad to fix things later, but it would be good if we had a common understanding before the change goes in.
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