Re: [Qemu-devel] vhost-user: VHOST_SET_MEM_TABLE, VHOST_SET_VRING_CALL need a reply?

[Michael S. Tsirkin]

On Thu, Sep 18, 2014 at 10:39:00AM +0800, Linhaifeng wrote:
> 
> 
> On 2014/9/17 17:56, Michael S. Tsirkin wrote:
> > On Wed, Sep 17, 2014 at 05:39:04PM +0800, Linhaifeng wrote:
> >> I think maybe is not need for the backend to wait for response.
> >>
> >> There is another way.vhost-user send "VHOST_GET_MEM_TABLE" to qemu then 
> >> qemu send VHOST_SET_MEM_TABLE to update the regions of vhost-user.same as 
> >> other command.
> >> If qemu could response the request of the vhost-user.the vhost-user could 
> >> update date at anytime.
> > 
> > The updates are initiated by QEMU, as a result of IOMMU,
> > memory hotplug or some other configuration change.
> 
> yes.when memory unplug/plug should tell vhost-user.

Right. So VHOST_SET_MEM_TABLE needs a response then, at least
for cases when it's freeing memory.

When memory is added, we can avoid waiting for the response
if vhost-user can detect a fault and flush the incoming
command pipe looking for VHOST_SET_MEM_TABLE.


> > 
> >> I think it's very useful for Commercialization.
> >>
> >> On 2014/9/17 16:38, Michael S. Tsirkin wrote:
> >>> Reply-To: 
> >>>
> >>> Thinking about the vhost-user protocol, VHOST_SET_MEM_TABLE
> >>> is used to update the memory mappings.
> >>>
> >>> So shouldn't we want for response?
> >>> Otherwise e.g. guest can start using the memory
> >>> that vhost-user can't access.
> >>>
> >>> Similarly, with an IOMMU vhost-user might access memory it shouldn't.
> >>>
> >>> VHOST_SET_VRING_CALL is used for MSI-X masking.
> >>> Again, after vector is masted by switching the call fd,
> >>> backend shouldn't assert the old one.
> >>>
> >>> Thoughts?
> >>>
> >>>
> > 
> > .
> >