netdev - Re: [MASSMAIL KLMS] Re: [RFC PATCH v1 0/7] virtio/vsock: introduce MSG

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Date:   Tue, 27 Jul 2021 12:34:36 +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>,
        Colin Ian King <colin.king@...onical.com>,
        Andra Paraschiv <andraprs@...zon.com>,
        Norbert Slusarek <nslusarek@....net>,
        "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>,
        "oxffffaa@...il.com" <oxffffaa@...il.com>
Subject: Re: [MASSMAIL KLMS] Re: [RFC PATCH v1 0/7] virtio/vsock: introduce
 MSG_EOR flag for SEQPACKET


On 27.07.2021 10:59, Stefano Garzarella wrote:
> Caution: This is an external email. Be cautious while opening links or attachments.
>
>
>
> On Mon, Jul 26, 2021 at 07:31:33PM +0300, Arseny Krasnov wrote:
>>       This patchset implements support of MSG_EOR bit for SEQPACKET
>> AF_VSOCK sockets over virtio transport.
>>       Idea is to distinguish concepts of 'messages' and 'records'.
>> 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.
>>       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.
> At this point it's probably better to rename the old flag, so we stay
> compatible.
>
> What happens if one of the two peers does not support MSG_EOR handling,
> while the other does?
>
> I'll do a closer review in the next few days.
Thank You, also i think MSG_EOR support must be described in spec
>
> Thanks,
> Stefano
>
>