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Subject: Re: [virtio-comment] [PATCH v4] virtio-vsock: add max payload size config field
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. > Also, do we have some sort of packets may not cross virtio buffer > boundaries, or even a single packet per single viritio buffer rule for > vsock. I did a quick search and could not find any. Did I overlook > something? Should we spell this out? > > @Michael, Conny: What do you think? > > Regards, > Halil
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