netdev - Re: [PATCH net-next v5 0/6] virtio/vsock: introduce MSG

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Date:   Mon, 6 Sep 2021 09:33:15 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Arseny Krasnov <arseny.krasnov@...persky.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Colin Ian King <colin.king@...onical.com>,
        Norbert Slusarek <nslusarek@....net>,
        Andra Paraschiv <andraprs@...zon.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: [PATCH net-next v5 0/6] virtio/vsock: introduce MSG_EOR flag for
 SEQPACKET

On Sun, Sep 05, 2021 at 04:18:52PM -0400, Michael S. Tsirkin wrote:
>On Sun, Sep 05, 2021 at 07:21:10PM +0300, Arseny Krasnov wrote:
>>
>> On 05.09.2021 19:19, Michael S. Tsirkin wrote:
>> > On Sun, Sep 05, 2021 at 07:02:44PM +0300, Arseny Krasnov wrote:
>> >> On 05.09.2021 18:55, Michael S. Tsirkin wrote:
>> >>> On Fri, Sep 03, 2021 at 03:30:13PM +0300, Arseny Krasnov wrote:
>> >>>> 	This patchset implements support of MSG_EOR bit for SEQPACKET
>> >>>> AF_VSOCK sockets over virtio transport.
>> >>>> 	First we need to define 'messages' and 'records' like this:
>> >>>> Message is result of sending calls: 'write()', 'send()', 'sendmsg()'
>> >>>> etc. It has fixed maximum length, and it bounds are visible using
>> >>>> return from receive calls: 'read()', 'recv()', 'recvmsg()' etc.
>> >>>> Current implementation based on message definition above.
>> >>>> 	Record has unlimited length, it consists of multiple message,
>> >>>> and bounds of record are visible via MSG_EOR flag returned from
>> >>>> 'recvmsg()' call. Sender passes MSG_EOR to sending system call and
>> >>>> receiver will see MSG_EOR when corresponding message will be processed.
>> >>>> 	Idea of patchset comes from POSIX: it says that SEQPACKET
>> >>>> supports record boundaries which are visible for receiver using
>> >>>> MSG_EOR bit. So, it looks like MSG_EOR is enough thing for SEQPACKET
>> >>>> and we don't need to maintain boundaries of corresponding send -
>> >>>> receive system calls. But, for 'sendXXX()' and 'recXXX()' POSIX says,
>> >>>> that all these calls operates with messages, e.g. 'sendXXX()' sends
>> >>>> message, while 'recXXX()' reads messages and for SEQPACKET, 'recXXX()'
>> >>>> must read one entire message from socket, dropping all out of size
>> >>>> bytes. Thus, both message boundaries and MSG_EOR bit must be supported
>> >>>> to follow POSIX rules.
>> >>>> 	To support MSG_EOR new bit was added along with existing
>> >>>> 'VIRTIO_VSOCK_SEQ_EOR': 'VIRTIO_VSOCK_SEQ_EOM'(end-of-message) - now it
>> >>>> works in the same way as 'VIRTIO_VSOCK_SEQ_EOR'. But 'VIRTIO_VSOCK_SEQ_EOR'
>> >>>> is used to mark 'MSG_EOR' bit passed from userspace.
>> >>>> 	This patchset includes simple test for MSG_EOR.
>> >>> I'm prepared to merge this for this window,
>> >>> but I'm not sure who's supposed to ack the net/vmw_vsock/af_vsock.c
>> >>> bits. It's a harmless variable renaming so maybe it does not matter.
>> >>>
>> >>> The rest is virtio stuff so I guess my tree is ok.
>> >>>
>> >>> Objections, anyone?
>> >> https://lkml.org/lkml/2021/9/3/76 this is v4. It is same as v5 in af_vsock.c changes.
>> >>
>> >> It has Reviewed by from Stefano Garzarella.
>> > Is Stefano the maintainer for af_vsock then?
>> > I wasn't sure.

I'm maintaining virtio-vsock stuff, but I'm reviewing most of the 
af_vsock patches. We don't have an entry for it in MAINTAINERS, maybe we 
should.

>> Ack, let's wait for maintainer's comment
>
>
>The specific patch is a trivial variable renaming so
>I parked this in my tree for now, will merge unless I
>hear any objections in the next couple of days.

I agree, I think your tree is fine, since this series is mostly about 
virtio-vsock.

Thanks,
Stefano