On Wed, May 31, 2017 at 08:15:26AM -0700, Stephen Hemminger wrote:

On Mon, 29 May 2017 15:42:17 +0200
Gaetan Rivet [off-list ref] wrote:

quoted

Periodically check for the existence of a device.
If a device has not been initialized and exists on the system, then it
is probed and configured.

The configuration process strives to synchronize the states between the
plugged-in sub-device and the fail-safe device.

There are existing event models (udev and netlink) that could be used to
do plug-in support without polling. Polling relies on application doing
rte_alarms and many don't.

Indeed. This possibility arose during development.

The main issue with it however is that it introduces an asynchronous
design, which the DPDK and PMDs underneath are not well-suited to
interact with. It goes against the grain in a way.

The polling is simple. It can work with all models of device and is
independent of event models specific to any architecture.

It also allows to simplify the contexts in which probing and
removal are done. Currently there is only one, the interrupt thread.
This solves a few possible race conditions without having to resort to
critical sections.

The only dependency is on another DPDK subsystem, rte_alarm.
I used alarms here because rte_timers need regular rte_timer_manage()
calls and there is little way to guarantee the frequency of the calls.

rte_alarms do not force any externalities on applications, thus allowing a
seamless use of the fail-safe.

-- 
Gaëtan Rivet
6WIND