[dpdk-dev] [PATCH] net/vhost: Add function to retreive the 'vid' for a given port id

[Wiles, Keith]

Regards,
Keith

> On Sep 23, 2016, at 12:26 AM, Yuanhan Liu <yuanhan.liu at linux.intel.com> wrote:
> 
> On Thu, Sep 22, 2016 at 06:43:55PM +0200, Thomas Monjalon wrote:
>>>>>>>> There could be a similar need in other PMD.
>>>>>>>> If we can get an opaque identifier of the device which is not the port id,
>>>>>>>> we could call some specific functions of the driver not implemented in
>>>>>>>> the generic ethdev API.
>>>>>>> 
>>>>>>> That means you have to add/export the PMD API first. Isn't it against what
>>>>>>> you are proposing -- "I think we should not add any API to the PMDs" ;)
>>>>>> 
>>>>>> Yes you are totally right :)
>>>>>> Except that in vhost case, we would not have any API in the PMD.
>>>>>> But it would allow to have some specific API in other PMDs for the features
>>>>>> which do not fit in a generic API.
>>>>> 
>>>>> So, does that mean you are okay with this patch now? I mean, okay to introduce
>>>>> a vhost PMD API?
>>>> 
>>>> It means I would be in favor of introducing API in drivers for very specific
>>>> features.
>>>> In this case, I am not sure that retrieving an internal id is very specific.
>>> 
>>> It's not, instead, it's very generic. The "internal id" is actually the
>>> public interface to vhost-user application, like "fd" to file APIs.
>>> 
>>> Instead of introducing a few specific wrappers/APIs, I'd prefer to
>>> introduce a generic one to get the handle, and let the application to
>>> call other vhost APIs.
>> 
>> Yes it makes sense.
>> I was thinking of introducing a function to get an internal id from ethdev,
>> in order to use it with any driver or underlying library.
>> But it would be an opaque pointer and you need an int.
>> Note that we can cast an int into a pointer, so I am not sure what is best.
> 
> Yes, that should work. But I just doubt what the "opaque pointer" could be
> for other PMD drivers, and what the application could do with it. For a
> typical nic PMD driver, I can think of nothing is valuable to export to
> user applications.
> 
> But maybe it's valuable to other virtual PMD drives as well, like the TAP
> pmd from Keith?

I do not see a need in the TAP PMD other then returning the FD for TUN/TAP device. Not sure what any application would need with the FD here, as it could cause some problems.

This feels like we are talking about a IOCTL like generic interface into the PMD. Then we can add new one types and reject types in the PMD that are not supported. Would this not be a better method for all future PMD APIs?

Here is just a thought as to how to solve this problem without a PMD specific API. A number of current ethdev APIs could be removed to use the API below. The APIs would be removed from ethdev structure and have the current APIs use the API below. I know some are not happy with number of APIs in the ethdev structure.

The API could be something like this:
struct rte_tlv {		/* Type/Length/Value like structure */
    uint16_t type;	/* Type of command */
    uint16_t len;         /* Length of data section on input and on output */
    uint16_t tlen;        /* Total or max length of data buffer */
    uint8_t data[0];
};

int rte_eth_dev_ioctl(int pid, int qid, struct rte_tlv *tlv);

> 
> If so, we may go that way.
> 
> Another thought is that, it may be a bit weird to me to introduce an API
> to get an opaque pointer. I mean, it's a bit hard to document it, because
> it has different meaning for different drivers. Should we list all of
> them then?
> 
> 	--yliu