Linux Virtualization - Mar 2023 - [RFC PATCH v2 2/4] virtio/vsock: remove all data from sk_buff

On Mon, Mar 06, 2023 at 07:00:10PM +0300, Arseniy Krasnov
wrote:
>
>
>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 at
sberdevices.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.
Thank you for checking it.

However, I still think it is better to use `hdr->len` (we have to assign 
it to `pkt_len` anyway, as in the proposal I sent for patch 1), 
otherwise we have to go every time to check if skb_* functions touch 
skb->len.

E.g. skb_pull() decrease skb->len, so I'm not sure we can call 
virtio_transport_dec_rx_pkt(skb->len) if we don't remove `skb_pull(skb, 
bytes_to_copy);` inside the loop.

Thanks,
Stefano