Re: [Qemu-devel] [RFC v1 6/9] virtio-crypto: rework virtio_crypto_handle_request

[Halil Pasic <pasic@linux.vnet.ibm.com>]

On 05/17/2017 11:12 AM, Gonglei (Arei) wrote:
>>>> By the way, I'm having a hard time understing how is the requirement form
>>>>
>> http://docs.oasis-open.org/virtio/virtio/v1.0/cs04/virtio-v1.0-cs04.html#x1-260
>>>> 004
>>>> (2.4.4 Message Framing) satisfied by this code. Could you explain this
>>>> to me please?
>>>>
>>> Sorry for my bad English,
>>> I don't know which normative formulation the code violates?
>> I'm not sure it's actually violated, but I'm concerned about the following
>> normative statement: "The device MUST NOT make assumptions about the
>> particular
>> arrangement of descriptors. The device MAY have a reasonable limit of
>> descriptors it will allow in a chain."
>>
>> Please also read the explanatory part I've linked, because the normative
>> statement is pretty abstract.
>>
>> In my understanding, the spec says, that e.g. the virti-crypto device
>> should not fail if a single request is split up into let's say two chunks
>> and transmitted by the means of two top level descriptors.
>>
>> Do you agree with my reading of the spec?
>>
> Yes, I agree. But what's the relationship about the request here?
> We don't assume the request have to use one desc entity, it can
> use scatter-gather list for one request header. 
> The device can cover the situation in the QEMU. 
> 
>> What does the virtio-crypto device do if it encounters such a situation?
>>
> This isn't a problem. Pls see blow code segment:
> 
> virtio_crypto_handle_request()
> {...
> if (unlikely(iov_to_buf(out_iov, out_num, 0, &req, sizeof(req))
>                 != sizeof(req))) {
>     virtio_error(vdev, "virtio-crypto request outhdr too short");
>     return -1;
> }
> iov_discard_front(&out_iov, &out_num, sizeof(req));
> ...
> 

Thats exactly what worries me. I see a call to virtio_error there...


void GCC_FMT_ATTR(2, 3) virtio_error(VirtIODevice *vdev, const char *fmt, ...)
{
    va_list ap;

    va_start(ap, fmt);
    error_vreport(fmt, ap);
    va_end(ap);

    vdev->broken = true;

    if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
        virtio_set_status(vdev, vdev->status | VIRTIO_CONFIG_S_NEEDS_RESET);
        virtio_notify_config(vdev);
    }
}

This however seems to make the device 'broken'. Or am I missing something?

Halil

> 
> Thanks,
> -Gonglei
>