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

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Date:   Sun, 5 Sep 2021 19:21:10 +0300
From:   Arseny Krasnov <arseny.krasnov@...persky.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...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 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.
Ack, let's wait for maintainer's comment
>
>>>
>>>>  Arseny Krasnov(6):
>>>>   virtio/vsock: rename 'EOR' to 'EOM' bit.
>>>>   virtio/vsock: add 'VIRTIO_VSOCK_SEQ_EOR' bit.
>>>>   vhost/vsock: support MSG_EOR bit processing
>>>>   virtio/vsock: support MSG_EOR bit processing
>>>>   af_vsock: rename variables in receive loop
>>>>   vsock_test: update message bounds test for MSG_EOR
>>>>
>>>>  drivers/vhost/vsock.c                   | 28 +++++++++++++----------
>>>>  include/uapi/linux/virtio_vsock.h       |  3 ++-
>>>>  net/vmw_vsock/af_vsock.c                | 10 ++++----
>>>>  net/vmw_vsock/virtio_transport_common.c | 23 ++++++++++++-------
>>>>  tools/testing/vsock/vsock_test.c        |  8 ++++++-
>>>>  5 files changed, 45 insertions(+), 27 deletions(-)
>>>>
>>>>  v4 -> v5:
>>>>  - Move bitwise and out of le32_to_cpu() in 0003.
>>>>
>>>>  v3 -> v4:
>>>>  - 'sendXXX()' renamed to 'send*()' in 0002- commit msg.
>>>>  - Comment about bit restore updated in 0003-.
>>>>  - 'same' renamed to 'similar' in 0003- commit msg.
>>>>  - u32 used instead of uint32_t in 0003-.
>>>>
>>>>  v2 -> v3:
>>>>  - 'virtio/vsock: rename 'EOR' to 'EOM' bit.' - commit message updated.
>>>>  - 'VIRTIO_VSOCK_SEQ_EOR' bit add moved to separate patch.
>>>>  - 'vhost/vsock: support MSG_EOR bit processing' - commit message
>>>>    updated.
>>>>  - 'vhost/vsock: support MSG_EOR bit processing' - removed unneeded
>>>>    'le32_to_cpu()', because input argument was already in CPU
>>>>    endianness.
>>>>
>>>>  v1 -> v2:
>>>>  - 'VIRTIO_VSOCK_SEQ_EOR' is renamed to 'VIRTIO_VSOCK_SEQ_EOM', to
>>>>    support backward compatibility.
>>>>  - use bitmask of flags to restore in vhost.c, instead of separated
>>>>    bool variable for each flag.
>>>>  - test for EAGAIN removed, as logically it is not part of this
>>>>    patchset(will be sent separately).
>>>>  - cover letter updated(added part with POSIX description).
>>>>
>>>> Signed-off-by: Arseny Krasnov <arseny.krasnov@...persky.com>
>>>> -- 
>>>> 2.25.1
>