linux-kernel - Re: [RFC PATCH v3 0/4] several updates to virtio/vsock

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Date:   Thu, 9 Mar 2023 17:32:00 +0100
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>,
        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 v3 0/4] several updates to virtio/vsock

On Thu, Mar 09, 2023 at 07:20:20PM +0300, Arseniy Krasnov wrote:
>
>
>On 09.03.2023 19:21, Stefano Garzarella wrote:
>> On Thu, Mar 09, 2023 at 01:10:36PM +0300, Arseniy Krasnov wrote:
>>> Hello,
>>>
>>> this patchset evolved from previous v2 version (see link below). It does
>>> several updates to virtio/vsock:
>>> 1) Changes 'virtio_transport_inc/dec_rx_pkt()' interface. Now instead of
>>>   using skbuff state ('head' and 'data' pointers) to update 'fwd_cnt'
>>>   and 'rx_bytes', integer value is passed as an input argument. This
>>>   makes code more simple, because in this case we don't need to udpate
>>>   skbuff state before calling 'virtio_transport_inc/dec_rx_pkt()'. In
>>>   more common words - we don't need to change skbuff state to update
>>>   'rx_bytes' and 'fwd_cnt' correctly.
>>> 2) For SOCK_STREAM, when copying data to user fails, current skbuff is
>>>   not dropped. Next read attempt will use same skbuff and last offset.
>>>   Instead of 'skb_dequeue()', 'skb_peek()' + '__skb_unlink()' are used.
>>>   This behaviour was implemented before skbuff support.
>>> 3) For SOCK_SEQPACKET it removes unneeded 'skb_pull()' call, because for
>>>   this type of socket each skbuff is used only once: after removing it
>>>   from socket's queue, it will be freed anyway.
>>>
>>> Test for 2) also added:
>>> Test tries to 'recv()' data to NULL buffer, then does 'recv()' with valid
>>> buffer. For SOCK_STREAM second 'recv()' must return data, because skbuff
>>> must not be dropped, but for SOCK_SEQPACKET skbuff will be dropped by
>>> kernel, and 'recv()' will return EAGAIN.
>>>
>>> Link to v1 on lore:
>>> https://lore.kernel.org/netdev/c2d3e204-89d9-88e9-8a15-3fe027e56b4b@sberdevices.ru/
>>>
>>> Link to v2 on lore:
>>> https://lore.kernel.org/netdev/a7ab414b-5e41-c7b6-250b-e8401f335859@sberdevices.ru/
>>>
>>> Change log:
>>>
>>> v1 -> v2:
>>> - For SOCK_SEQPACKET call 'skb_pull()' also in case of copy failure or
>>>   dropping skbuff (when we just waiting message end).
>>> - Handle copy failure for SOCK_STREAM in the same manner (plus free
>>>   current skbuff).
>>> - Replace bug repdroducer with new test in vsock_test.c
>>>
>>> v2 -> v3:
>>> - Replace patch which removes 'skb->len' subtraction from function
>>>   'virtio_transport_dec_rx_pkt()' with patch which updates functions
>>>   'virtio_transport_inc/dec_rx_pkt()' by passing integer argument
>>>   instead of skbuff pointer.
>>> - Replace patch which drops skbuff when copying to user fails with
>>>   patch which changes this behaviour by keeping skbuff in queue until
>>>   it has no data.
>>> - Add patch for SOCK_SEQPACKET which removes redundant 'skb_pull()'
>>>   call on read.
>>> - I remove "Fixes" tag from all patches, because all of them now change
>>>   code logic, not only fix something.
>>
>> Yes, but they solve the problem, so we should use the tag (I think at
>> least in patch 1 and 3).
>>
>> We usually use the tag when we are fixing a problem introduced by a
>> previous change. So we need to backport the patch to the stable branches
>> as well, and we need the tag to figure out which branches have the patch
>> or not.
>Ahh, sorry. Ok. I see now :)

No problem at all :-)

I think also patch 2 can have the Fixes tag.

Thanks,
Stefano

>
>Thanks, Arseniy
>>
>> Thanks,
>> Stefano
>>
>>>
>>> Arseniy Krasnov (4):
>>>  virtio/vsock: don't use skbuff state to account credit
>>>  virtio/vsock: remove redundant 'skb_pull()' call
>>>  virtio/vsock: don't drop skbuff on copy failure
>>>  test/vsock: copy to user failure test
>>>
>>> net/vmw_vsock/virtio_transport_common.c |  29 +++---
>>> tools/testing/vsock/vsock_test.c        | 118 ++++++++++++++++++++++++
>>> 2 files changed, 131 insertions(+), 16 deletions(-)
>>>
>>> -- 
>>> 2.25.1
>>>
>>
>