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

[Stefano Stabellini]

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!


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