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

From: "Loftus, Ciara" <ciara.loftus@intel.com>
To: Yuanhan Liu <yuanhan.liu@linux.intel.com>,
	Thomas Monjalon <thomas.monjalon@6wind.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>, "Wiles, Keith" <keith.wiles@intel.com>
Subject: Re: [PATCH] net/vhost: Add function to retreive the 'vid' for a given port id
Date: Fri, 23 Sep 2016 09:26:23 +0000	[thread overview]
Message-ID: <74F120C019F4A64C9B78E802F6AD4CC24F95A8BB@IRSMSX106.ger.corp.intel.com> (raw)
In-Reply-To: <20160923091609.GC23158@yliu-dev.sh.intel.com>

> 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.

My hope would be have this, or at least some way to access rte_vhost_get_queue_num(vid) from the PMD in 16.11. We can't integrate the PMD into OVS until we achieve this. Is this likely at this stage given the uncertainty around the API?

Thanks,
Ciara

> 
> > > 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