Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready

[David Gibson]

On Thu, 22 Oct 2020 16:55:10 +0300
Marcel Apfelbaum <marcel.apfelbaum@gmail.com> wrote:

> Hi David, Michael,
> 
> On Thu, Oct 22, 2020 at 3:56 PM David Gibson <dgibson@redhat.com> wrote:
> 
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> > > Probably the only way to handle for existing machine types.  
> >  
> 
> I agree
> 
> 
> > > For new ones, can't we queue it in host memory somewhere?  
> >
> >  
> I am not sure I understand what will be the flow.
>   - The user asks for a hotplug operation.
>   -  QEMU deferred operation.
> After that the operation may still fail, how would the user know if the
> operation
> succeeded or not?
> 
> 
> 
> > I'm not actually convinced we can't do that even for existing machine
> > types.  
> 
> 
> Is a Guest visible change, I don't think we can do it.

How is it a guest visible change?

> > So I'm a bit hesitant to suggest going ahead with this without
> > looking a bit closer at whether we can implement a wait-for-ready in
> > qemu, rather than forcing every user of qemu (human or machine) to do
> > so.
> 
> While I agree it is a pain from the usability point of view, hotplug
> operations
> are allowed to fail. This is not more than a corner case, ensuring the right
> response (gracefully erroring out) may be enough.
> 
> Thanks,
> Marcel
> 
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-- 
David Gibson <dgibson@redhat.com>
Principal Software Engineer, Virtualization, Red Hat

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