Re: [Qemu-devel] [PATCH V14 5/7] Add a TPM Passthrough backend driver implementation

[Stefan Berger]

On 02/20/2012 04:30 PM, Michael S. Tsirkin wrote:
> On Wed, Dec 14, 2011 at 08:43:20AM -0500, Stefan Berger wrote:
> > +
> > +static void *tpm_passthrough_thread(void *d)
> > +{
> > +    TPMPassthruThreadParams *thr_parms = d;
> > +    TPMPassthruState *tpm_pt = thr_parms->tb->s.tpm_pt;
> > +    uint32_t in_len;
> > +
> > +    dprintf("tpm_passthrough: THREAD IS STARTING\n");
> > +
> > +    /* start command processing */
> > +    while (!tpm_pt->thread_terminate) {
> IMO you want to checvk thread_terminate undet a lock/

The way the termination flag is used along with the condition it isn't 
necessary to call it with a lock held. It may run into the condition but 
then be woken up with a signal and then again check the flag and terminate.

> > +        /* receive and handle commands */
> > +        in_len = 0;
> > +        do {
> > +            dprintf("tpm_passthrough: waiting for commands...\n");
> > +
> > +            if (tpm_pt->thread_terminate) {
> > +                break;
> > +            }
> > +
> This will have to be duplicate in each backend, no?

There is this sequence of code around the condition that helps us 
waiting for the front-end to send a command that is indeed repeated in 
every backend. I isolated that now but would like to keep the general 
thread more flexible and inside the individual backends. There is quite 
some code that is different in every backend.


> So I would say make this logic part of backend
> and expose some api.

Ok, a single function for now:

void tpm_backend_wait_for_command(TPMState *tpm_state);


> You can then call it from backend or invoke
> backend callbacks from frontend.

 I was only going to invoke it from within the backend thread.


   Stefan