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

[Yuanhan Liu]

On Wed, Sep 14, 2016 at 09:10:48AM +0200, Thomas Monjalon wrote:
> 2016-09-14 12:43, Yuanhan Liu:
> > On Tue, Sep 13, 2016 at 05:10:09PM +0200, Thomas Monjalon wrote:
> > > 2016-09-13 14:47, Ciara Loftus:
> > > > In some cases when using the vHost PMD, certain vHost library functions
> > > > may still need to be accessed. One such example is the
> > > > rte_vhost_get_queue_num function which returns the number of virtqueues
> > > > reported by the guest - information which is not exposed by the PMD.
> > > > 
> > > > This commit introduces a new rte_eth_vhost function that returns the
> > > > 'vid' associated with a given port id. This allows the PMD user to call
> > > > vHost library functions which require the 'vid' value.
> > > 
> > > I think we should not add any API to the PMDs.
> > 
> > In general, I agree with you.
> > 
> > > Maybe you are looking for a generic API in ethdev.
> > 
> > But maybe it's a bit hard to define a "right" generic API here. For this
> > case, the generic API I can think of could be:
> > 
> > - an API to get queue num, like rte_eth_get_queue_enabled_num
> >   I barely know NIC pmd drivers, but I doubt it's useful/meaningful for them.
> > 
> > - an API to get a PMD driver private (or specific) data.
> >   For vhost-pmd, it's vid. Again, I don't know what it could be for other nic
> >   drivers.
> > 
> >   This one may be a better option here, because it expose a key field to
> >   the application, vid, with which the application can invoke more vhost
> >   APIs. And apparently, it's not feasible to try to define a generic API
> >   for some (if not each) vhost APIs.
> 
> 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" ;)

	--yliu