Re: [RFC PATCH v2 2/4] virtio/vsock: remove all data from sk_buff

[Stefano Garzarella]

On Mon, Mar 06, 2023 at 07:00:10PM +0300, Arseniy Krasnov wrote:
> On 06.03.2023 18:51, Stefano Garzarella wrote:
> > On Mon, Mar 06, 2023 at 06:31:22PM +0300, Arseniy Krasnov wrote:
> > > On 06.03.2023 15:08, Stefano Garzarella wrote:
> > > > On Sun, Mar 05, 2023 at 11:07:37PM +0300, Arseniy Krasnov wrote:
> > > > > In case of SOCK_SEQPACKET all sk_buffs are used once - after read some
> > > > > data from it, it will be removed, so user will never read rest of the
> > > > > data. Thus we need to update credit parameters of the socket like whole
> > > > > sk_buff is read - so call 'skb_pull()' for the whole buffer.
> > > > >
> > > > > Fixes: 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff")
> > > > > Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
> > > > > ---
> > > > > net/vmw_vsock/virtio_transport_common.c | 2 +-
> > > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > Maybe we could avoid this patch if we directly use pkt_len as I
> > > > suggested in the previous patch.
> > > Hm, may be we can avoid calling 'skb_pull()' here if 'virtio_transport_dec_rx_pkt()'
> > > will use integer argument?
> >
> > Yep, exactly!
> >
> > > Just call 'virtio_transport_dec_rx_pkt(skb->len)'. skb
> >
> > It depends on how we call virtio_transport_inc_rx_pkt(). If we use
> > hdr->len there I would use the same to avoid confusion. Plus that's the
> > value the other peer sent us, so definitely the right value to increase
> > fwd_cnt with. But if skb->len always reflects it, then that's fine.
> i've checked 'virtio_transport_rx_work()', it calls 'virtio_vsock_skb_rx_put()' which
> sets 'skb->len'. Value is used from header, so seems 'skb->len' == 'hdr->len' in this
> case.

Thank you for checking it.

However, I still think it is better to use `hdr->len` (we have to assign 
it to `pkt_len` anyway, as in the proposal I sent for patch 1), 
otherwise we have to go every time to check if skb_* functions touch 
skb->len.

E.g. skb_pull() decrease skb->len, so I'm not sure we can call 
virtio_transport_dec_rx_pkt(skb->len) if we don't remove `skb_pull(skb, 
bytes_to_copy);` inside the loop.

Thanks,
Stefano