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

[Yuanhan Liu]

On Fri, Sep 23, 2016 at 10:43:20AM +0200, Thomas Monjalon wrote:
> 2016-09-23 12:26, Yuanhan Liu:
> > 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?
> > 
> > If so, we may go that way.
> 
> I would like to have more opinions/votes before proceeding.

Sure, fair enough. There is no rush.

> > 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?
> 
> I think it can be documented in API using this handler how it can
> be retrieved. In your case, the vhost lib can explain that the vid
> is retrieved from the PMD with this generic ethdev function.

Okay.

	--yliu