Re: [dpdk-dev] [PATCH] eal: bus scan and probe never fail

[Thomas Monjalon <thomas@monjalon.net>]

10/10/2017 18:00, Aaron Conole:
> Shreyansh Jain <shreyansh.jain@nxp.com> writes:
> 
> > Hello Don,
> >
> > On Monday 09 October 2017 11:51 PM, Don Provan wrote:
> >>> -----Original Message-----
> >>> From: Shreyansh Jain [mailto:shreyansh.jain@nxp.com]
> >>> Sent: Monday, October 09, 2017 4:10 AM
> >>> To: Jan Blunck <jblunck@infradead.org>; Thomas Monjalon
> >>> <thomas@monjalon.net>
> >>> Cc: dev <dev@dpdk.org>; Hemant Agrawal <hemant.agrawal@nxp.com>
> >>> Subject: Re: [dpdk-dev] [PATCH] eal: bus scan and probe never fail
> >>>
> >>> ...
> >>> This is where I have disagreement/doubt.
> >>> Reporting error code from rte_bus_scan would do two things:
> >>>
> >>> 1. rte_eal_init is not designed to ignore/log-only these errors - it
> >>> would quit initialization. (But, this can be changed)
> >>> 2. What should rte_eal_init do with this error? rte_bus_scan would have
> >>> already printed the problematic bus->scan() failure.
> >>
> >> These practical problems confirm to me that the failure of a bus
> >> scan is more of a strategic issue: when asking "which devices can
> >> I use?", "none" is a perfectly valid answer that does not seem
> >> like an error to me even when a failed bus scan is the reason for
> >> that answer.
> >
> > I agree with this.
> >
> >>
> >>  From the application's point of view, the potential error here
> >> is that the device it wants to use isn't available. I don't see that
> >> either the init function or the probe function will have enough
> >> information to understand that application-level problem, so
> >> they should leave it to the application to detect it.
> >
> > I think I understand you comment but just want to cross check again:
> > Scan or probe error should simply be ignored by EAL layer and let the
> > application take stance when it detects that the device it was looking
> > for is missing. Is my understanding correct?
> >
> > I am trying to come a conclusion so that this patch can either be
> > modified or pushed as it is. If the above understanding is correct, I
> > don't see any changes required in the patch.
> 
> Does it make sense to introduce a way to query the results of the
> various bus types for their status?  That way we can give the relevant
> information to the application if it wants, and make the bus scanning
> code *always* succeed?  This version shouldn't be an ABI breakage,
> either (confirm?).
> 
> half-baked below (not tested or suitable - just an example):

We are going to need notification callbacks for scan and probe anyway.
I think errors could be also notified with callbacks?