[dpdk-dev] [PATCH v3 3/5] bus/vdev: bus scan by multi-process channel

Tan, Jianfeng jianfeng.tan at intel.com
Fri Apr 20 17:32:25 CEST 2018



On 4/20/2018 11:19 PM, Burakov, Anatoly wrote:
> On 20-Apr-18 3:28 PM, Tan, Jianfeng wrote:
>>
>>
>> On 4/20/2018 4:41 PM, Burakov, Anatoly wrote:
>>> On 19-Apr-18 5:50 PM, Jianfeng Tan wrote:
>>>> To scan the vdevs in primary, we send request to primary process
>>>> to obtain the names for vdevs.
>>>>
>>>> Only the name is shared from the primary. In probe(), the device
>>>> driver is supposed to locate (or request more) the detail
>>>> information from the primary.
>>>>
>>>> Signed-off-by: Jianfeng Tan <jianfeng.tan at intel.com>
>>>> Reviewed-by: Qi Zhang <qi.z.zhang at intel.com>
>>>> ---
>>>
>>> <...>
>>>
>>>> +static int
>>>> +vdev_action(const struct rte_mp_msg *mp_msg, const void *peer)
>>>> +{
>>>> +    struct rte_vdev_device *dev;
>>>> +    struct rte_mp_msg mp_resp;
>>>> +    struct vdev_param *ou = (struct vdev_param *)&mp_resp.param;
>>>> +    const struct vdev_param *in = (const struct vdev_param 
>>>> *)mp_msg->param;
>>>> +    const char *devname;
>>>> +    int num;
>>>> +
>>>> +    strcpy(mp_resp.name, "vdev");
>>>> +    mp_resp.len_param = sizeof(*ou);
>>>> +    mp_resp.num_fds = 0;
>>>> +
>>>> +    switch (in->type) {
>>>> +    case VDEV_SCAN_REQ:
>>>> +        ou->type = VDEV_SCAN_ONE;
>>>> +        ou->num = 1;
>>>> +        num = 0;
>>>> +
>>>> +        rte_spinlock_lock(&vdev_device_list_lock);
>>>> +        TAILQ_FOREACH(dev, &vdev_device_list, next) {
>>>> +            devname = rte_vdev_device_name(dev);
>>>> +            if (strlen(devname) == 0)
>>>> +                VDEV_LOG(INFO, "vdev with no name is not sent");
>>>> +            VDEV_LOG(INFO, "send vdev, %s", devname);
>>>> +            strncpy(ou->name, devname, RTE_DEV_NAME_MAX_LEN);
>>>
>>> Probably better use strlcpy as it always null-terminates.
>>
>> Yep.
>>
>>>
>>>> +            if (rte_mp_sendmsg(&mp_resp) < 0)
>>>> +                VDEV_LOG(ERR, "send vdev, %s, failed, %s",
>>>> +                     devname, strerror(rte_errno));
>>>> +            num++;
>>>
>>> Some comments on what is going on here (why are we sending messages 
>>> in response? why multiple? who will receive these messages?) would 
>>> be nice.
>>
>> Yep, will explain that below.
>>
>>> I have a sneaking suspicion that you could've packed the response 
>>> into one single message, but i'm not completely sure what is going 
>>> on here, so maybe what you have here makes sense...
>>
>> What's happening here is that:
>>
>> a. Secondary process sends a sync request to ask for vdev in primary.
>> b. Primary process receives the request, and send vdevs one by one.
>> c. Primary process sends back reply, which indicates how many vdevs 
>> are sent.
>>
>> The reason we don't pack all vdevs in the reply message is that, the 
>> message length is RTE_MP_MAX_PARAM_LEN (256) in length. It's possible 
>> that we cannot pack all vdevs in the single reply message.
>>
>
> OK. How does secondary know which vdevs are new and which aren't?

This auto discovery is designed for secondary boot to know which vdevs 
are used in primary. So they are all new to the secondary process. For 
runtime vdev add in primary, we are going to rely on hotplug framework 
to tell the news to secondary processes.

> Does it even matter how many vdevs primary has sent? Correct me if i'm 
> wrong, but it seems that you're only using sync request as kind of 
> synchronization mechanism, and are not actually expecting any useful 
> data in the reply. Which is OK, but in that case just don't bother 
> sending any data in the reply in the first place :)

I would like to keep this information, so that secondary process can 
tell how many vdevs come from primary process (secondary process can 
definitely iterate the vdev list to know, but it's that straightforward).

Thanks,
Jianfeng



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