linux-kernel - Re: [RFC PATCH v1 0/4] virtio/vsock: some updates for MSG

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Message-ID: <bb1c0271-bd0d-7a2d-01a8-b7777af67017@sberdevices.ru>
Date:   Tue, 27 Jun 2023 14:58:57 +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>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...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 v1 0/4] virtio/vsock: some updates for MSG_PEEK flag



On 26.06.2023 19:30, Stefano Garzarella wrote:
> On Sun, Jun 18, 2023 at 09:24:47AM +0300, Arseniy Krasnov wrote:
>> Hello,
>>
>> This patchset does several things around MSG_PEEK flag support. In
>> general words it reworks MSG_PEEK test and adds support for this flag
>> in SOCK_SEQPACKET logic. Here is per-patch description:
>>
>> 1) This is cosmetic change for SOCK_STREAM implementation of MSG_PEEK:
>>   1) I think there is no need of "safe" mode walk here as there is no
>>      "unlink" of skbs inside loop (it is MSG_PEEK mode - we don't change
>>      queue).
>>   2) Nested while loop is removed: in case of MSG_PEEK we just walk
>>      over skbs and copy data from each one. I guess this nested loop
>>      even didn't behave as loop - it always executed just for single
>>      iteration.
>>
>> 2) This adds MSG_PEEK support for SOCK_SEQPACKET. It could be implemented
>>   be reworking MSG_PEEK callback for SOCK_STREAM to support SOCK_SEQPACKET
>>   also, but I think it will be more simple and clear from potential
>>   bugs to implemented it as separate function thus not mixing logics
>>   for both types of socket. So I've added it as dedicated function.
>>
>> 3) This is reworked MSG_PEEK test for SOCK_STREAM. Previous version just
>>   sent single byte, then tried to read it with MSG_PEEK flag, then read
>>   it in normal way. New version is more complex: now sender uses buffer
>>   instead of single byte and this buffer is initialized with random
>>   values. Receiver tests several things:
>>   1) Read empty socket with MSG_PEEK flag.
>>   2) Read part of buffer with MSG_PEEK flag.
>>   3) Read whole buffer with MSG_PEEK flag, then checks that it is same
>>      as buffer from 2) (limited by size of buffer from 2) of course).
>>   4) Read whole buffer without any flags, then checks that is is same
>>      as buffer from 3).
>>
>> 4) This is MSG_PEEK test for SOCK_SEQPACKET. It works in the same way
>>   as for SOCK_STREAM, except it also checks combination of MSG_TRUNC
>>   and MSG_PEEK.
>>
>> Head is:
>> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d20dd0ea14072e8a90ff864b2c1603bd68920b4b
> 
> Nice cleanup, LGTM, but I'd like a comment from Bobby.

Got it, thanks!

Thanks, Arseniy

> 
> Thanks,
> Stefano
>