Re: [dpdk-dev] [PATCH v4 04/19] vhost: fix payload size of reply

[Tiwei Bie <tiwei.bie@intel.com>]

On Tue, Oct 09, 2018 at 12:34:28PM +0200, Maxime Coquelin wrote:
> On 10/09/2018 12:30 PM, Maxime Coquelin wrote:
> > On 10/09/2018 12:21 PM, Tiwei Bie wrote:
> > > On Mon, Oct 08, 2018 at 05:25:42PM +0200, Maxime Coquelin wrote:
> > > > QEMU doesn't expect any payload for the reply of
> > > > VHOST_USER_SET_LOG_BASE request, so don't send any.
> > > > Note that the Vhost-user specification isn't clear about
> > > > it and would need to be fixed.
> > > > 
> > > > Fixes: 54f9e32305d4 ("vhost: handle dirty pages logging request")
> > > > Cc: stable@dpdk.org
> > > > 
> > > > Reported-by: Ilya Maximets <i.maximets@samsung.com>
> > > > Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> > > > Acked-by: Ilya Maximets <i.maximets@samsung.com>
> > > > ---
> > > >   lib/librte_vhost/vhost_user.c | 6 +++++-
> > > >   1 file changed, 5 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/lib/librte_vhost/vhost_user.c
> > > > b/lib/librte_vhost/vhost_user.c
> > > > index 7f3e86778..71a0e7dd7 100644
> > > > --- a/lib/librte_vhost/vhost_user.c
> > > > +++ b/lib/librte_vhost/vhost_user.c
> > > > @@ -1296,7 +1296,11 @@ vhost_user_set_log_base(struct virtio_net
> > > > **pdev, struct VhostUserMsg *msg)
> > > >       dev->log_base = dev->log_addr + off;
> > > >       dev->log_size = size;
> > > > -    msg->size = sizeof(msg->payload.u64);
> > > > +    /*
> > > > +     * The spec is not clear about it (yet), but QEMU doesn't expect
> > > > +     * any payload in the reply.
> > > > +     */
> > > > +    msg->size = 0;
> > > 
> > > I think the spec is clear about it that no payload is
> > > expected in the reply:
> > > 
> > > https://github.com/qemu/qemu/blob/7c69b7c84964/docs/interop/vhost-user.txt#L496
> > > 
> > It isn't really clear because there are two cases[0]:
> > 1. VHOST_USER_PROTOCOL_F_LOG_SHMFD not negotiated: In this case no reply
> >     has to be sent.
> > 2. VHOST_USER_PROTOCOL_F_LOG_SHMFD negotiated: In this case reply with
> >     empty payload hsa to be sent.
> > 
> > [0]: https://github.com/qemu/qemu/blob/7c69b7c849641a39ba3defa40d384a2ba24cd7a2/docs/interop/vhost-user.txt#L177
> > 
> 
> And I would add that N/A isn't clear, because SET_VRING_ADDR specifies
> N/A as slave payload, whereas the implementation does not implement a
> reply.

Good point.

> 
> > > But below line in the spec needs to be fixed:
> > > 
> > > https://github.com/qemu/qemu/blob/7c69b7c84964/docs/interop/vhost-user.txt#L495
> > > 
> > 
> > Indeed.
> > 
> > > 
> > > >       return VH_RESULT_REPLY;
> > > >   }
> > > > -- 
> > > > 2.17.1
> > > >