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

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

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.

	--yliu