linux-kernel - Re: [RFC PATCH v8 00/19] virtio/vsock: introduce SOCK

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Message-ID: <20210422084638.bvblk33b4oi6cec6@steredhat>
Date:   Thu, 22 Apr 2021 10:46:38 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseny Krasnov <arseny.krasnov@...persky.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jorgen Hansen <jhansen@...are.com>,
        Colin Ian King <colin.king@...onical.com>,
        Andra Paraschiv <andraprs@...zon.com>,
        Norbert Slusarek <nslusarek@....net>,
        Alexander Popov <alex.popov@...ux.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stsp2@...dex.ru" <stsp2@...dex.ru>,
        "oxffffaa@...il.com" <oxffffaa@...il.com>
Subject: Re: [RFC PATCH v8 00/19] virtio/vsock: introduce SOCK_SEQPACKET
 support

On Wed, Apr 21, 2021 at 06:06:28PM +0300, Arseny Krasnov wrote:
>On 21.04.2021 12:52, Stefano Garzarella wrote:
>> On Tue, Apr 13, 2021 at 03:39:51PM +0300, Arseny Krasnov wrote:
>>> v7 -> v8:
>>> General changelog:
>>> - whole idea is simplified: channel now considered reliable,
>>>   so SEQ_BEGIN, SEQ_END, 'msg_len' and 'msg_id' were removed.
>>>   Only thing that is used to mark end of message is bit in
>>>   'flags' field of packet header: VIRTIO_VSOCK_SEQ_EOR. Packet
>>>   with such bit set to 1 means, that this is last packet of
>>>   message.
>>>
>>> - POSIX MSG_EOR support is removed, as there is no exact
>>>   description how it works.
>> It would be nice to support it, I'll try to see if I can find anything.
>>
>> I just reviewed the series. I think the most important things to fix are
>> the `seqpacket_allow` stored in the struct virtio_transport that is
>> wrong IMHO, and use cpu_to_le32()/le32_to_cpu() to access the flags.
>
>Thank You, i'll prepare next version. Main question is: does this
>approach(no SEQ_BEGIN, SEQ_END, 'msg_len' and 'msg_id') considered
>good? In this case it will be easier to prepare final version, because 
>is smaller and more simple than previous logic. Also patch to spec
>will be smaller.

Yes, it's definitely much better than before.

The only problem I see is that we add some overhead per fragment 
(header). We could solve that with the mergeable buffers that Jiang is 
considering for DGRAM.

If we have that support, I think we could reuse it here as well, but it 
might be a next step.

Thanks,
Stefano