Linux Virtualization - Jun 2023 - [RFC PATCH v1 2/4] virtio/vsock: support MSG_PEEK for SOCK_SEQPACKET

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 at sberdevices.ru>
>>> ---
>>> 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
>>>
>>
>