Re: [PATCH] tpm: add backend for mssim

[Daniel P . Berrangé]

On Mon, Dec 12, 2022 at 05:06:05PM -0500, James Bottomley wrote:
> On Mon, 2022-12-12 at 15:47 +0000, Daniel P. Berrangé wrote:
> > Copy'ing Markus for QAPI design feedback.
> > 
> > On Sat, Dec 10, 2022 at 12:10:18PM -0500, James Bottomley wrote:
> [...]
> > > +##
> > > +# @TPMmssimOptions:
> > > +#
> > > +# Information for the mssim emulator connection
> > > +#
> > > +# @host: host name or IP address to connect to
> > > +# @port: port for the standard TPM commands
> > > +# @ctrl: control port for TPM state changes
> > > +#
> > > +# Since: 7.2.0
> > > +##
> > > +{ 'struct': 'TPMmssimOptions',
> > > +  'data': {
> > > +      'host': 'str',
> > > +      'port': 'str',
> > > +      'ctrl': 'str' },
> > > +  'if': 'CONFIG_TPM' }
> > 
> > We don't want to be adding new code using plain host/port combos,
> > as that misses extra functionality for controlling IPv4 vs IPv6
> > usage.
> > 
> > The existing 'emulator' backend references a chardev, but I'm
> > not especially in favour of using the chardev indirection either,
> > when all we should really need is a SocketAddress
> > 
> > IOW, from a QAPI design POV, IMHO the best practice would be
> > 
> >  { 'struct': 'TPMmssimOptions',
> >    'data': {
> >        'command': 'SocketAddress',
> >        'control': 'SocketAddress' },
> >    'if': 'CONFIG_TPM' }
> > 
> > 
> > The main wrinkle with this is that exprssing nested struct fields
> > with QemuOpts is a disaster zone, and -tpmdev doesn't yet support
> > JSON syntax.
> > 
> > IMHO we should just fix the latter problem, as I don't think it
> > ought to be too hard. Probably a cut+paste / search/replace job
> > on the chanmge we did for -device in:
> > 
> >   commit 5dacda5167560b3af8eadbce5814f60ba44b467e
> >   Author: Kevin Wolf <kwolf@redhat.com>
> >   Date:   Fri Oct 8 15:34:42 2021 +0200
> > 
> >     vl: Enable JSON syntax for -device
> > 
> > This would mean we could use plain -tpmdev for a local instance
> > 
> >    -tpmdev mssim,id=tpm0 \
> >     -device tpm-crb,tpmdev=tpm0 \
> > 
> > but to use a remote emulator we would use
> > 
> >     -tpmdev "{'backend': 'mssim', 'id': 'tpm0',
> >               'command': {
> >                  'type': 'inet',
> >                  'host': 'remote',
> >                  'port': '4455'
> >                },
> >               'control': {
> >                  'type': 'inet',
> >                  'host': 'remote',
> >                  'port': '4456'
> >                }}"
> > 
> > (without the whitepace/newlines, which i just used for sake of
> > clarity)
> 
> Just on this, might it not be easier for the commandline to do what
> gluster does?  just use the '.' as a separator and subqdict extraction,
> so you'd specify
> 
> -tpmdev 
> mssim,id=tpm0,command.type=inet,command.host=remote,command.port=4455,control.type=inet,control.host=remote,control.port=4456
> 
> With the added bonus that X.type could be defaulted to inet and
> control.host could follow command.host and so on?

These days, we have a policy of not tyring to map nested data onto the
flat QemuOpts. This has been done in several areas and we've ended up
with a mess of ever so slightly different impls each with their own
flaws. This is why our preferred approach these days is to add support
for JSON syntax to enable non-flat config.


With regards,
Daniel
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