linux-kernel - Re: [PATCH RFC v3 1/6] exterr: Introduce extended syscall error reporting

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Date:	Tue, 15 Sep 2015 19:02:19 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Jonathan Corbet <corbet@....net>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	vince@...ter.net, eranian@...gle.com,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	linux-api@...r.kernel.org
Subject: Re: [PATCH RFC v3 1/6] exterr: Introduce extended syscall error
 reporting


> I think that anything other than the errno "grab it now or lose it"
> behavior will prove confusing.  I don't think there is any other way to
> know that a given error report corresponds to a specific system call.
> Library calls can mess it up.  Kernel changes adding extended reporting to
> new system calls can mess it up.  Applications cannot possibly be expected
> to know which system calls might change the error-reporting status, they
> *have* to assume all of them will.
> 

Yeah I was about to say something similar - an application that expects
a certain syscall to have extended errors will get confused if running
on an older kernel where that syscall in fact does *not* have extended
errors (and thus also doesn't clear extended errors) and therefore the
extended error from a previous syscall could still be lingering on (for
example because the application didn't care to fetch it for that previo
us syscall.)

johannes
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