Re: [Qemu-devel] [PATCH v5 1/4] Provide support for the CUSE TPM

[Michael S. Tsirkin]

On Wed, Mar 01, 2017 at 05:20:13PM +0000, Daniel P. Berrange wrote:
> > > > > QEMU's defined the vhost-user ABI/API and delegated
> > > > > impl to something else.
> > > > The vhost ABI isn't easy to maintain at all though. So I would not
> > > > commit to that lightly without a good reason.
> > > > 
> > > > It will be way more painful if the ABI is dictated by a 3rd party
> > > > library.
> > > 
> > > Who should define it?
> > 
> > No one. Put it in same source tree with QEMU and forget ABI stability
> > issues.
> 
> That doesn't work very well in practice as you have to make sure the
> vTPM process that is running, provides exactly the same ABI as the QEMU
> process that's connecting to it. You could have a single vTPM process
> on the host serving many QEMU processes, each of which could be a
> different QEMU version, due to upgraded RPMs/Debs.
> 
> Regards,
> Daniel

I might be wrong but last time I looked each QEMU instance had to use
its own CUSE device. So the pain seems entirely self-inflicted, you
could have a process per QEMU instance, start and stop it from within
QEMU.


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