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

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

On Fri, Sep 23, 2016 at 09:23:11PM +0000, Wiles, Keith wrote:
> 
> Regards,
> Keith
> 
> > On Sep 23, 2016, at 12:26 AM, Yuanhan Liu <yuanhan.liu@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.

Yes, that's what I meant.

> Not sure what any application would need with the FD here, as it could cause some problems.

Me, neither.

> 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);

Looks like a very clean solution to me!

Thomas?

	--yliu
> 
> > 
> > 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