linux-kernel - Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting

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Message-Id: <20150826114111.01675d8eadda78d82933d8a5@linux-foundation.org>
Date:	Wed, 26 Aug 2015 11:41:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Johannes Berg <johannes@...solutions.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>, adrian.hunter@...el.com,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Vince Weaver <vince@...ter.net>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting

On Wed, 26 Aug 2015 09:26:56 +0200 Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Ingo Molnar <mingo@...nel.org> wrote:
> 
> > ... but back then I didn't feel like complicating an error recovery ABI for the 
> > needs of the 1%, robust error handling is all about simplicity: if it's not 
> > simple, tools won't use it.
> 
> And note that it needs to be 'simple' in two places for usage to grow naturally: 
> 
>   - the usage site in the kernel
>   - the tooling side that recovers the information.
> 
> That's why I think that such a form:
> 
> 	return err_str(-EINVAL, "x86/perf: CPU does not support precise sampling");
> 
> is obviously simple on the kernel side as it returns -EINVAL, and is very simple 
> on the tooling side as well, if we are allowed to extend prctl().
> 

Is this whole thing overkill?  As far as I can see, the problem which is
being addressed only occurs in a couple of places (perf, wifi netlink
handling) and could be addressed with some local pr_debug statements.  ie,

#define err_str(e, s) ({
	if (debugging)
		pr_debug("%s:%d: error %d (%s)", __FILE__, __LINE__, e, s);
	e;
})

(And I suppose that if this is later deemed inadequate, err_str() could
be made more fancy).


IOW, do we really need some grand kernel-wide infrastructural thing to
adequately address this problem?

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