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

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

On 3/10/2016 2:34 PM, Tetsuya Mukawa wrote:
> On 2016/03/10 15:25, Tan, Jianfeng wrote:
>>
>> On 3/10/2016 2:14 PM, Tetsuya Mukawa wrote:
>>> Currently, default value of kickfd and callfd is -1.
>>> If the value is -1, current code guess kickfd and callfd hasn'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 value to -2. And the
>>> patch defines -2 as VIRTIO_UNINITIALIZED_EVENTFD.
>>>
>>> Signed-off-by: Tetsuya Mukawa <mukawa@igel.co.jp>
>>> ---
>>>    lib/librte_vhost/rte_virtio_net.h             | 1 +
>>>    lib/librte_vhost/vhost_user/virtio-net-user.c | 7 ++++---
>>>    lib/librte_vhost/virtio-net.c                 | 4 ++--
>>>    3 files changed, 7 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/lib/librte_vhost/rte_virtio_net.h
>>> b/lib/librte_vhost/rte_virtio_net.h
>>> index 7d1fde2..d745707 100644
>>> --- a/lib/librte_vhost/rte_virtio_net.h
>>> +++ b/lib/librte_vhost/rte_virtio_net.h
>>> @@ -89,6 +89,7 @@ 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)
>>>        int            callfd;            /**< Used to notify the guest
>>> (trigger interrupt). */
>>>        int            kickfd;            /**< Currently unused as
>>> polling mode is enabled. */
>>>        int            enabled;
>>> diff --git a/lib/librte_vhost/vhost_user/virtio-net-user.c
>>> b/lib/librte_vhost/vhost_user/virtio-net-user.c
>>> index 65b5652..591f9bf 100644
>>> --- a/lib/librte_vhost/vhost_user/virtio-net-user.c
>>> +++ b/lib/librte_vhost/vhost_user/virtio-net-user.c
>>> @@ -225,8 +225,8 @@ static int
>>>    vq_is_ready(struct vhost_virtqueue *vq)
>>>    {
>>>        return vq && vq->desc   &&
>>> -           vq->kickfd != -1 &&
>>> -           vq->callfd != -1;
>>> +           vq->kickfd != VIRTIO_UNINITIALIZED_EVENTFD &&
>>> +           vq->callfd != VIRTIO_UNINITIALIZED_EVENTFD;
>>>    }
>>>      static int
>>> @@ -318,7 +318,8 @@ user_get_vring_base(struct vhost_device_ctx ctx,
>>>         */
>>>        if (dev->virtqueue[state->index]->kickfd >= 0) {
>>>            close(dev->virtqueue[state->index]->kickfd);
>> Then -1 will be a valid value, need to check if it's not -1 to
>> close()? Nevertheless, close(-1) brings no big problem.
>>
> We did it in above 'if' condition checking, then close(-1) will not be
> called.

Sorry, missed that. So when kickfd == -1, need to be set to 
VIRTIO_UNINITIALIZED_EVENTFD?

Thanks,
Jianfeng

>
> Thanks,
> Tetsuya
>
>> Thanks,
>> Jianfeng
>>
>>> -        dev->virtqueue[state->index]->kickfd = -1;
>>> +        dev->virtqueue[state->index]->kickfd =
>>> +                    VIRTIO_UNINITIALIZED_EVENTFD;
>>>        }
>>>          return 0;
>>> diff --git a/lib/librte_vhost/virtio-net.c
>>> b/lib/librte_vhost/virtio-net.c
>>> index fe1a77e..3498e9d 100644
>>> --- a/lib/librte_vhost/virtio-net.c
>>> +++ b/lib/librte_vhost/virtio-net.c
>>> @@ -263,8 +263,8 @@ init_vring_queue(struct vhost_virtqueue *vq, int
>>> qp_idx)
>>>    {
>>>        memset(vq, 0, sizeof(struct vhost_virtqueue));
>>>    -    vq->kickfd = -1;
>>> -    vq->callfd = -1;
>>> +    vq->kickfd = VIRTIO_UNINITIALIZED_EVENTFD;
>>> +    vq->callfd = VIRTIO_UNINITIALIZED_EVENTFD;
>>>          /* Backends are set to -1 indicating an inactive device. */
>>>        vq->backend = -1;