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

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Message-ID: <9b882d45-3d9d-c44d-a172-f23fff54962b@sberdevices.ru>
Date:   Mon, 6 Mar 2023 19:00:10 +0300
From:   Arseniy Krasnov <avkrasnov@...rdevices.ru>
To:     Stefano Garzarella <sgarzare@...hat.com>
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>,
        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 v2 2/4] virtio/vsock: remove all data from sk_buff



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@...rdevices.ru>
>>>> ---
>>>> 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.
> 
>> is never returned to queue to read it again, so i think may be there is no sense for
>> extra call 'skb_pull'?
> 
> Right!
> 
> Thanks,
> Stefano
>