Re: [PATCH] tpm: add backend for mssim

[James Bottomley <jejb@linux.ibm.com>]

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?

James