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

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Date:   Sun, 5 Sep 2021 12:19:56 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Arseny Krasnov <arseny.krasnov@...persky.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 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.

> >
> >
> >>  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
> >