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

[Aaron Conole]

Thomas Monjalon <thomas at monjalon.net> writes:

> 10/10/2017 18:00, Aaron Conole:
>> Shreyansh Jain <shreyansh.jain at nxp.com> writes:
>> 
>> > Hello Don,
>> >
>> > On Monday 09 October 2017 11:51 PM, Don Provan wrote:
>> >>> -----Original Message-----
>> >>> From: Shreyansh Jain [mailto:shreyansh.jain at nxp.com]
>> >>> Sent: Monday, October 09, 2017 4:10 AM
>> >>> To: Jan Blunck <jblunck at infradead.org>; Thomas Monjalon
>> >>> <thomas at monjalon.net>
>> >>> Cc: dev <dev at dpdk.org>; Hemant Agrawal <hemant.agrawal at 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?

Definitely.  That's part of my half-baked patch.  Call the error check
function and get a callback.  There's probably a better way to do it
than my patch.