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

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Message-ID: <a1788ed6-89d4-27da-a049-99e29edea4cb@sberdevices.ru>
Date:   Thu, 9 Mar 2023 19:20:20 +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 v3 0/4] several updates to virtio/vsock



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 :)

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
>>
>