Re: [PATCH v2] vhost: Fix default value of kickfd and callfd

[Tetsuya Mukawa <mukawa@igel.co.jp>]

On 2016/03/14 17:21, Yuanhan Liu wrote:
> On Mon, Mar 14, 2016 at 04:54:00PM +0900, Tetsuya Mukawa wrote:
>> On 2016/03/14 11:08, Yuanhan Liu wrote:
>>> On Mon, Mar 14, 2016 at 10:54:14AM +0900, Tetsuya Mukawa wrote:
>>>> On 2016/03/11 16:19, Yuanhan Liu wrote:
>>>>> On Thu, Mar 10, 2016 at 04:06:05PM +0900, Tetsuya Mukawa wrote:
>>>>>> Currently, default values of kickfd and callfd are -1.
>>>>>> If the values are -1, current code guesses kickfd and callfd haven't
>>>>>> been initialized yet. And vhost library will guess the virtqueue isn't
>>>>>> ready for processing.
>>>>>> But callfd and kickfd will be set as -1 when "--enable-kvm"
>>>>>> isn't specified in QEMU command line. It means we cannot treat -1 as
>>>>>> uninitialized state. The patch changes default values to -2. And the
>>>>>> patch defines -2 as VIRTIO_UNINITIALIZED_EVENTFD.
>>>>> This looks more like a workaround to me. 
>>>> Hi Yuanhan,
>>>>
>>>> Sorry for late reply.
>>>> I have checked QEMU documentation, and found below.
>>>>
>>>> ----------
>>>>  * VHOST_USER_SET_VRING_CALL
>>>>
>>>>       Id: 14
>>>>       Equivalent ioctl: VHOST_SET_VRING_CALL
>>>>       Master payload: u64
>>>>
>>>>       Set the event file descriptor to signal when buffers are used. It
>>>>       is passed in the ancillary data.
>>>>       Bits (0-7) of the payload contain the vring index. Bit 8 is the
>>>>       invalid FD flag.
>>>> ----------
>>>>
>>>> VHOST_USER_SET_VRING_KICK has almost same description.
>>>> I will check this invalid flag, and if it works for our case, then will
>>>> use it.
>>>> How about it?
>>> Yeah, that indeed sounds much better.
>> I've checked current dpdk code.
>> It seems we've already checked invalid flag like below.
>>
>>         if (pmsg->payload.u64 & VHOST_USER_VRING_NOFD_MASK)
>>                 file.fd = -1;
>>         else
>>                 file.fd = pmsg->fds[0];
>>
>> So how about adding below macros or enum?
>>
>> #define VIRTIO_UNINITIALIZED_EVENTFD   (-2)
>> #define VIRTIO_INVALID_EVENTFD              (-1)
>>
>> I am still not sure whether using enum is better or not.
> Both are Okay to me; I have no preference on that.
>
>> But here is one of example patch.
>> What do you think?
> Looks okay to me
>
>> diff --git a/lib/librte_vhost/rte_virtio_net.h
>> b/lib/librte_vhost/rte_virtio_net.h
>> index 7d1fde2..2a7566d 100644
>> --- a/lib/librte_vhost/rte_virtio_net.h
>> +++ b/lib/librte_vhost/rte_virtio_net.h
>> @@ -89,6 +89,8 @@ struct vhost_virtqueue {
>>         uint16_t                vhost_hlen;             /**< Vhost
>> header length (varies depending on RX merge buffers. */
>>         volatile uint16_t       last_used_idx;          /**< Last index
>> used on the available ring */
>>         volatile uint16_t       last_used_idx_res;      /**< Used for
>> multiple devices reserving buffers. */
>> +#define VIRTIO_UNINITIALIZED_EVENTFD   (-2)
>> +#define VIRTIO_INVALID_EVENTFD         (-1)
> One nit: you may keep it in order.

Thanks for  your comments, will change it.

Tetsuya

> 	--yliu