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Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages to support virtio config space |
Date: |
Fri, 20 Oct 2017 05:12:11 +0300 |
On Fri, Oct 20, 2017 at 01:55:20AM +0000, Liu, Changpeng wrote:
>
>
> > -----Original Message-----
> > From: Michael S. Tsirkin [mailto:address@hidden
> > Sent: Friday, October 20, 2017 8:28 AM
> > To: Paolo Bonzini <address@hidden>
> > Cc: Liu, Changpeng <address@hidden>; address@hidden;
> > address@hidden; address@hidden; address@hidden; Harris,
> > James R <address@hidden>
> > Subject: Re: [PATCH v4 1/4] vhost-user: add new vhost user messages to
> > support
> > virtio config space
> >
> > On Thu, Oct 19, 2017 at 11:04:48PM +0200, Paolo Bonzini wrote:
> > > On 19/10/2017 19:43, Michael S. Tsirkin wrote:
> > > > On Thu, Oct 19, 2017 at 05:43:18PM +0200, Paolo Bonzini wrote:
> > > >> On 19/10/2017 17:39, Michael S. Tsirkin wrote:
> > > >>>> Add VHOST_USER_GET_CONFIG/VHOST_USER_SET_CONFIG messages
> > which can be
> > > >>>> used for live migration of vhost user devices, also vhost user
> > > >>>> devices
> > > >>>> can benefit from the messages to get/set virtio config space from/to
> > > >>>> the
> > > >>>> I/O target. For the purpose to support virtio config space change,
> > > >>>> VHOST_USER_SET_CONFIG_FD message is added as the event notifier
> > > >>>> in case virtio config space change in the I/O target.
> > > >>>>
> > > >>>> Signed-off-by: Changpeng Liu <address@hidden>
> > > >>> I don't much like it that config is getting passed through.
> > > >>>
> > > >>> IMO this makes managing things harder not easier.
> > > >>>
> > > >>> How about specific messages about specific parts of
> > > >>> config space that you want to get from the backend?
> > > >>
> > > >> In the case of virtio-blk that would be all of it. Do you have a case
> > > >> in mind where some part of the configuration space is owned by QEMU?
> > > >>
> > > >> Paolo
> > > >
> > > > Yes. seg_max
> > >
> > > The seg_max limit is established by whoever reads buffers from the vring
> > > and passes them down to the lower layer. For vhost-blk that's the
> > > device server, not QEMU.
> > >
> > > Paolo
> >
> > Good point. How about num_queues though?
> num_queues is part of virtio_blk config, vhost-user slave can set it,
> and Qemu driver can rewrite it if user want less IO queues.
Fundamentally QEMU needs to support this # of queues for this
device.
So whenever QEMU doesn't always expose config space as-is,
need to document the exact semantics.
Also, does backend need to know?
> >
> > Also why is there SET_CONFIG? Does not look like blk uses it.
> Only one possible usage when disable write cache to vhost-user slave device.
Again need to add documentation what can be written.
> >
> > And I wonder how do we do it for other devices.
> >
> > E.g. for net there's a bit in the middle of the
> > config field that deals with migration.
> Well, I'm okay to make those messages only valid for virtio block device,
> because it's enough
> for virtio block to be started with vhost-user slave target.
OK but I'd rather make them at least somewhat generic so we can reuse
them down the road. It looks like adding offset/size pair would solve
most of the issues. Thoughts?
> >
> >
> > --
> > MST
- Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages to support virtio config space, (continued)
Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages to support virtio config space, Michael S. Tsirkin, 2017/10/19
- Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages to support virtio config space, Paolo Bonzini, 2017/10/19
- Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages to support virtio config space, Michael S. Tsirkin, 2017/10/19
- Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages to support virtio config space, Paolo Bonzini, 2017/10/19
- Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages to support virtio config space, Michael S. Tsirkin, 2017/10/19
- Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages to support virtio config space, Liu, Changpeng, 2017/10/19
- Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages to support virtio config space,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH v4 1/4] vhost-user: add new vhost user messages to support virtio config space, Liu, Changpeng, 2017/10/19
[Qemu-devel] [PATCH v4 2/4] vhost-user-blk: introduce a new vhost-user-blk host device, Changpeng Liu, 2017/10/19
- Re: [Qemu-devel] [PATCH v4 2/4] vhost-user-blk: introduce a new vhost-user-blk host device, Paolo Bonzini, 2017/10/19
- Re: [Qemu-devel] [PATCH v4 2/4] vhost-user-blk: introduce a new vhost-user-blk host device, Stefan Hajnoczi, 2017/10/19
- Re: [Qemu-devel] [PATCH v4 2/4] vhost-user-blk: introduce a new vhost-user-blk host device, Liu, Changpeng, 2017/10/19
- Re: [Qemu-devel] [PATCH v4 2/4] vhost-user-blk: introduce a new vhost-user-blk host device, Stefan Hajnoczi, 2017/10/20
- Re: [Qemu-devel] [PATCH v4 2/4] vhost-user-blk: introduce a new vhost-user-blk host device, Liu, Changpeng, 2017/10/23
- Re: [Qemu-devel] [PATCH v4 2/4] vhost-user-blk: introduce a new vhost-user-blk host device, Michael S. Tsirkin, 2017/10/23
- Re: [Qemu-devel] [PATCH v4 2/4] vhost-user-blk: introduce a new vhost-user-blk host device, Liu, Changpeng, 2017/10/23