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

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Message-ID: <20210727095803.s26subp3pgclqzvi@steredhat>
Date:   Tue, 27 Jul 2021 11:58:03 +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>,
        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 Tue, Jul 27, 2021 at 12:34:36PM +0300, Arseny Krasnov wrote:
>
>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

Yep, sure!

What do you think about the concerns above?

Stefano