linux-kernel - Re: [PATCH] lib: vsprintf: add printf format conversion %M for errno strings

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Date:   Tue, 27 Jun 2017 13:02:59 +0200
From:   Bernd Petrovitsch <bernd@...rovitsch.priv.at>
To:     Randy Dunlap <rdunlap@...radead.org>,
        "Enrico Weigelt, metux IT consult" <enrico.weigelt@...3.net>,
        Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib: vsprintf: add printf format conversion %M for
 errno strings

Hi all!

On Sun, 2017-06-25 at 15:47 -0700, Randy Dunlap wrote:
> On 06/25/2017 02:18 PM, Enrico Weigelt, metux IT consult wrote:
> > On 25.06.2017 22:10, Joe Perches wrote:
> > 
> > > > 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.

That is hard-coded in gcc ATM TTBOMK (AFAIK BSDs ship patched gcc's for
their in-kernel extensions of format strings).

> > > Everything else uses "%p<foo>", <object reference>
> > 
> > hmm, but errno's aren't pointers. Isn't %p checked for pointer
> > values ?

Yup, and gcc will also generate a format string warning/error.

> > > > Already was about to do so. Shall I call it strerror() ?
> > > 
> > > I presume kstrerror
> > > 
> > > So use something like
> > > 	"%d: (%s)", errno, kstrerror(errno)
> > 
> > Okay, sounds good.
> 
> but why not just do that in userspace. Sure, you can keep that as your
> internal kernel patch, but there's not really much need for it to be in the
> mainline kernel.  So when your driver prints "blah: foo bar error 49",
> just run a little program that converts 49 to <whatever>.

Userspace can just guess if a given "49" is an errno or not ...

MfG,
	Bernd
-- 
Bernd Petrovitsch                  Email : bernd@...rovitsch.priv.at
                     LUGA : http://www.luga.at