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Date:   Tue, 27 Jun 2023 09:48:06 +0200
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Arseniy Krasnov <avkrasnov@sberdevices.ru>
Cc:     Stefan Hajnoczi <stefanha@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Bobby Eshleman <bobby.eshleman@bytedance.com>,
        kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel@sberdevices.ru, oxffffaa@gmail.com
Subject: Re: [RFC PATCH v1 2/4] virtio/vsock: support MSG_PEEK for
 SOCK_SEQPACKET
Message-ID: <4pcexfrdtuisz53c4sb4pse4cyjw7zsuwtqsnnul23njo4ab5l@4jvdk6buxmj3>
References: <20230618062451.79980-1-AVKrasnov@sberdevices.ru>
 <20230618062451.79980-3-AVKrasnov@sberdevices.ru>
 <yiy3kssoiyzs6ehnlo7g2xsb26zee5vih3jpgyc7i3dvfcyfpv@xvokxez3lzpo>
 <9553a82f-ce31-e2e0-ff62-8abd2a6b639b@sberdevices.ru>
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In-Reply-To: <9553a82f-ce31-e2e0-ff62-8abd2a6b639b@sberdevices.ru>
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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@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
>>>
>>
>