Re: [RFC PATCH v8 00/19] virtio/vsock: introduce SOCK_SEQPACKET support

From: Stefano Garzarella <sgarzare@redhat.com>
To: Arseny Krasnov <arseny.krasnov@kaspersky.com>
Cc: Andra Paraschiv <andraprs@amazon.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"stsp2@yandex.ru" <stsp2@yandex.ru>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"virtualization@lists.linux-foundation.org"
	<virtualization@lists.linux-foundation.org>,
	"oxffffaa@gmail.com" <oxffffaa@gmail.com>,
	Norbert Slusarek <nslusarek@gmx.net>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Colin Ian King <colin.king@canonical.com>,
	Jakub Kicinski <kuba@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jorgen Hansen <jhansen@vmware.com>,
	Alexander Popov <alex.popov@linux.com>
Subject: Re: [RFC PATCH v8 00/19] virtio/vsock: introduce SOCK_SEQPACKET support
Date: Thu, 22 Apr 2021 10:46:38 +0200	[thread overview]
Message-ID: <20210422084638.bvblk33b4oi6cec6@steredhat> (raw)
In-Reply-To: <2c3d0749-0f41-e064-0153-b6130268add2@kaspersky.com>

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

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