linux-kernel - Re: [RFC PATCH v1 2/4] virtio/vsock: support MSG_PEEK for SOCK

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Date:   Tue, 27 Jun 2023 09:48:06 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseniy Krasnov <avkrasnov@...rdevices.ru>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Bobby Eshleman <bobby.eshleman@...edance.com>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...rdevices.ru, oxffffaa@...il.com
Subject: Re: [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@...rdevices.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
>>>
>>
>