[dpdk-dev] [PATCH v6 05/11] bus: introduce hotplug functionality

[Thomas Monjalon]

28/06/2017 13:58, Jan Blunck:
> On Wed, Jun 28, 2017 at 1:44 PM, Thomas Monjalon <thomas at monjalon.net> wrote:
> > 27/06/2017 21:03, Jan Blunck:
> >> On Tue, Jun 27, 2017 at 6:11 PM, Gaetan Rivet <gaetan.rivet at 6wind.com> wrote:
> >> > --- a/lib/librte_eal/common/include/rte_bus.h
> >> > +++ b/lib/librte_eal/common/include/rte_bus.h
> >> >  /**
> >> > + * Implementation specific probe function which is responsible for linking
> >> > + * devices on that bus with applicable drivers.
> >> > + * The plugged device might already have been used previously by the bus,
> >> > + * in which case some buses might prefer to detect and re-use the relevant
> >> > + * information pertaining to this device.
> >> > + *
> >> > + * @param da
> >> > + *     Device declaration.
> >> > + *
> >> > + * @return
> >> > + *     The pointer to a valid rte_device usable by the bus on success.
> >> > + *     NULL on error. rte_errno is then set.
> >> > + */
> >> > +typedef struct rte_device * (*rte_bus_plug_t)(struct rte_devargs *da);
> >>
> >> Shouldn't this be orthogonal to unplug() and take a rte_device. You
> >> should only be able to plug devices that have been found by scan
> >> before.
> >
> > Plugging a device that has been scanned before is a special case.
> > In a true hotplug scenario, we could use this plug function passing
> > a devargs.
> > I don't see any issue passing rte_devargs to plug and rte_device to unplug.
> 
> What do you mean by "true hotplug"?

I mean a kernel notification of a new device.

> The problem with this is that passing just rte_devargs to plug()
> requires the bus to parse and enrich the rte_devargs with bus
> specifics. From there it gets folded into the to-be-created bus
> specific rte_XXX_device. This makes it unnecessarily complicated and
> even worse it adds a second code path how devices come alive.

Just after the notification, the rte_device does not exist yet.
So the plug function could share the same code as the scan function
to get the metadata and create the device instance.

> When we get notified about a hotplug event we already know which bus
> this event belongs to:
> 
> 1. scan the bus for incoming devices

No need to scan every devices here.

> 2. plug single device with devargs and probe for drivers
> 
> Makes sense?

I want to make sure there is no misunderstanding first :)