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

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Date:   Thu, 22 Apr 2021 12:40:17 +0300
From:   Arseny Krasnov <arseny.krasnov@...persky.com>
To:     Stefano Garzarella <sgarzare@...hat.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 22.04.2021 11:46, Stefano Garzarella wrote:
> 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 are talking about receive, i think, i can reuse merge logic for

stream sockets, the only difference is that buffers are mergeable

until previous EOR(e.g. previous message) bit is found in rx queue.

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