Re: [RFC PATCH v1 2/4] virtio/vsock: support MSG_PEEK for SOCK_SEQPACKET

[Stefano Garzarella]

On Tue, Jun 27, 2023 at 07:34:29AM +0300, Arseniy Krasnov wrote:
> On 26.06.2023 19:28, Stefano Garzarella wrote:
> > On Sun, Jun 18, 2023 at 09:24:49AM +0300, Arseniy Krasnov wrote:
> > > This adds support of MSG_PEEK flag for SOCK_SEQPACKET type of socket.
> > > Difference with SOCK_STREAM is that this callback returns either length
> > > of the message or error.
> > >
> > > Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
> > > ---
> > > net/vmw_vsock/virtio_transport_common.c | 63 +++++++++++++++++++++++--
> > > 1 file changed, 60 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> > > index 2ee40574c339..352d042b130b 100644
> > > --- a/net/vmw_vsock/virtio_transport_common.c
> > > +++ b/net/vmw_vsock/virtio_transport_common.c
> > > @@ -460,6 +460,63 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> > >     return err;
> > > }
> > >
> > > +static ssize_t
> > > +virtio_transport_seqpacket_do_peek(struct vsock_sock *vsk,
> > > +                   struct msghdr *msg)
> > > +{
> > > +    struct virtio_vsock_sock *vvs = vsk->trans;
> > > +    struct sk_buff *skb;
> > > +    size_t total, len;
> > > +
> > > +    spin_lock_bh(&vvs->rx_lock);
> > > +
> > > +    if (!vvs->msg_count) {
> > > +        spin_unlock_bh(&vvs->rx_lock);
> > > +        return 0;
> > > +    }
> > > +
> > > +    total = 0;
> > > +    len = msg_data_left(msg);
> > > +
> > > +    skb_queue_walk(&vvs->rx_queue, skb) {
> > > +        struct virtio_vsock_hdr *hdr;
> > > +
> > > +        if (total < len) {
> > > +            size_t bytes;
> > > +            int err;
> > > +
> > > +            bytes = len - total;
> > > +            if (bytes > skb->len)
> > > +                bytes = skb->len;
> > > +
> > > +            spin_unlock_bh(&vvs->rx_lock);
> > > +
> > > +            /* sk_lock is held by caller so no one else can dequeue.
> > > +             * Unlock rx_lock since memcpy_to_msg() may sleep.
> > > +             */
> > > +            err = memcpy_to_msg(msg, skb->data, bytes);
> > > +            if (err)
> > > +                return err;
> > > +
> > > +            spin_lock_bh(&vvs->rx_lock);
> > > +        }
> > > +
> > > +        total += skb->len;
> > > +        hdr = virtio_vsock_hdr(skb);
> > > +
> > > +        if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOM) {
> > > +            if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOR)
> > > +                msg->msg_flags |= MSG_EOR;
> > > +
> > > +            break;
> > > +        }
> > > +    }
> > > +
> > > +    spin_unlock_bh(&vvs->rx_lock);
> > > +
> > > +    return total;
> >
> > Should we return the minimum between total and len?
>
> I guess no, because seqpacket dequeue callback always returns length of message,
> then, in af_vsock.c we return either number of bytes read or length of message
> depending on MSG_TRUNC flags.

Right! We should always return the total lenght of the packet.

Thanks,
Stefano

> Thanks, Arseniy
>
> > Thanks,
> > Stefano
> >
> > > +}
> > > +
> > > static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
> > >                          struct msghdr *msg,
> > >                          int flags)
> > > @@ -554,9 +611,9 @@ virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk,
> > >                    int flags)
> > > {
> > >     if (flags & MSG_PEEK)
> > > -        return -EOPNOTSUPP;
> > > -
> > > -    return virtio_transport_seqpacket_do_dequeue(vsk, msg, flags);
> > > +        return virtio_transport_seqpacket_do_peek(vsk, msg);
> > > +    else
> > > +        return virtio_transport_seqpacket_do_dequeue(vsk, msg, flags);
> > > }
> > > EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_dequeue);
> > >
> > > -- 
> > > 2.25.1