Re: [Xen-devel] [v3 3/5] Qemu-Xen-vTPM: Register Xen stubdom vTPM frontend driver

["Xu, Quan" <quan.xu@xxxxxxxxx>]

> -----Original Message-----
> From: Stefano Stabellini [mailto:stefano.stabellini@xxxxxxxxxxxxx]
> Sent: Tuesday, January 20, 2015 1:19 AM
> To: Xu, Quan
> Cc: qemu-devel@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxx;
> stefano.stabellini@xxxxxxxxxxxxx
> Subject: Re: [v3 3/5] Qemu-Xen-vTPM: Register Xen stubdom vTPM frontend
> driver
> 
> On Tue, 30 Dec 2014, Quan Xu wrote:
> > +int vtpm_recv(struct XenDevice *xendev, uint8_t* buf, size_t *count)
> > +{
> > +    struct xen_vtpm_dev *vtpmdev = container_of(xendev, struct
> xen_vtpm_dev,
> > +                                                xendev);
> > +    struct tpmif_shared_page *shr = vtpmdev->shr;
> > +    unsigned int offset;
> > +
> > +    if (shr->state == TPMIF_STATE_IDLE) {
> > +        return -ECANCELED;
> > +    }
> > +
> > +    while (vtpm_status(vtpmdev) != VTPM_STATUS_IDLE) {
> > +        vtpm_aio_wait(vtpm_aio_ctx);
> > +    }
> 
> Is this really necessary to write this as a busy loop?
> I think you should write it as a proper aio callback for efficiency:
> QEMU is going to burn 100% of the cpu polling and not doing anything else!

I agree.
I will improve it in v4.

-Quan
> 
> 
> > +    offset = sizeof(*shr) + 4*shr->nr_extra_pages;
> > +    memcpy(buf, offset + (uint8_t *)shr, shr->length);
> > +    *count = shr->length;
> > +
> > +    return 0;
> > +}

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