Re: [PATCH RFC net-next v4 6/8] virtio/vsock: support dgrams

[Stefano Garzarella]

On Sun, Jun 11, 2023 at 11:49:02PM +0300, Arseniy Krasnov wrote:
> Hello Bobby!
>
> On 10.06.2023 03:58, Bobby Eshleman wrote:
> > This commit adds support for datagrams over virtio/vsock.
> >
> > Message boundaries are preserved on a per-skb and per-vq entry basis.
>
> I'm a little bit confused about the following case: let vhost sends 4097 bytes
> datagram to the guest. Guest uses 4096 RX buffers in it's virtio queue, each
> buffer has attached empty skb to it. Vhost places first 4096 bytes to the first
> buffer of guests RX queue, and 1 last byte to the second buffer. Now IIUC guest
> has two skb in it rx queue, and user in guest wants to read data - does it read
> 4097 bytes, while guest has two skb - 4096 bytes and 1 bytes? In seqpacket there is
> special marker in header which shows where message ends, and how it works here?

I think the main difference is that DGRAM is not connection-oriented, so
we don't have a stream and we can't split the packet into 2 (maybe we
could, but we have no guarantee that the second one for example will be
not discarded because there is no space).

So I think it is acceptable as a restriction to keep it simple.

My only doubt is, should we make the RX buffer size configurable,
instead of always using 4k?

Thanks,
Stefano