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

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

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