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Message-ID: <1498421449.24295.39.camel@perches.com>
Subject: Re: [PATCH] lib: vsprintf: add printf format conversion %M for
 errno strings
From: Joe Perches <joe@perches.com>
To: "Enrico Weigelt, metux IT consult" <enrico.weigelt@gr13.net>,
        linux-kernel@vger.kernel.org
Date: Sun, 25 Jun 2017 13:10:49 -0700
In-Reply-To: <6a12988d-bbcc-54e7-be16-eeeb94f88d57@gr13.net>
References: <20170625171230.7613-1-enrico.weigelt@gr13.net>
         <1498411624.24295.36.camel@perches.com>
         <6a12988d-bbcc-54e7-be16-eeeb94f88d57@gr13.net>
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On Sun, 2017-06-25 at 21:53 +0200, Enrico Weigelt, metux IT consult
wrote:
> On 25.06.2017 19:27, Joe Perches wrote:
> 
> > Every use of %M is going to cause gcc when using __printf to emit
> > a warning like:
> > 
> > unknown conversion type character ‘M’ in format [-Wformat=]
> 
> Yeah, that's still an open problem. Actually, I still haven't found out,
> how it's done w/ all the other kernel-internal conversions.

Everything else uses "%p<foo>", <object reference>

> I was under
> the impression, there was some magic to tell the compiler which letters
> correspond to which types - unfortunately, didn't find anything like
> that. Is that really hardcoded in gcc ?
> 
> > Beyond that, why is this useful?
> 
> Use that instead of %d where errno values are printed/logged.
> > There can't possibly be any fast-path use.
> 
> I'm using it eg. for driver development - always having to look up the
> numbers is quite ugly and time consuming.
> 
> > Why not just create a function that does errno/string conversions?
> 
> Already was about to do so. Shall I call it strerror() ?

I presume kstrerror

So use something like
	"%d: (%s)", errno, kstrerror(errno)