Re: [PATCH] tpm: Return QMP error when TPM is disabled in build

[Daniel P . Berrangé]

On Wed, Jun 09, 2021 at 07:34:32PM +0200, Philippe Mathieu-Daudé wrote:
> On 6/9/21 7:27 PM, Philippe Mathieu-Daudé wrote:
> > On 6/9/21 6:01 PM, Marc-André Lureau wrote:
> >> Hi
> >>
> >> On Wed, Jun 9, 2021 at 7:33 PM Philippe Mathieu-Daudé <philmd@redhat.com
> >> <mailto:philmd@redhat.com>> wrote:
> >>
> >>     When the management layer queries a binary built using --disable-tpm
> >>     for TPM devices, it gets confused by getting empty responses:
> >>
> >>       { "execute": "query-tpm" }
> >>       {
> >>           "return": [
> >>           ]
> >>       }
> >>       { "execute": "query-tpm-types" }
> >>       {
> >>           "return": [
> >>           ]
> >>       }
> >>       { "execute": "query-tpm-models" }
> >>       {
> >>           "return": [
> >>           ]
> >>       }
> >>
> >>     Make it clearer by returning an error, mentioning the feature is
> >>     disabled:
> >>
> >>       { "execute": "query-tpm" }
> >>       {
> >>           "error": {
> >>               "class": "GenericError",
> >>               "desc": "this feature or command is not currently supported"
> >>           }
> >>       }
> >>
> >>     Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com
> >>     <mailto:philmd@redhat.com>>
> >>
> >>
> >> Why not make the qapi schema conditional?
> 
> Using your suggestion (and ignoring QAPI marshaling error) I'm getting:
> 
> { "execute": "query-tpm" }
> {
>     "error": {
>         "class": "CommandNotFound",
>         "desc": "The command query-tpm has not been found"
>     }
> }
> 
> Is that OK from a management perspective?

That's fairly typical of what we'd expect to see from a feature
which is either removed at compile time, or never existed in the first
place. mgmt apps don't really need to distinguish those two scenarios,
so this is fine.

Regards,
Daniel
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