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Date: Tue, 14 May 2019 14:37:51 -0400
From: Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] vsprintf: Do not break early boot with probing
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To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: David Laight <David.Laight@aculab.com>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Petr Mladek <pmladek@suse.com>, Andy Shevchenko <andriy.shevchenko@linux.intel.com>, christophe leroy <christophe.leroy@c-s.fr>, Linus Torvalds <torvalds@linux-foundation.org>, Rasmus Villemoes <linux@rasmusvillemoes.dk>, "Tobin C . Harding" <me@tobin.cc>, Michal Hocko <mhocko@suse.cz>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Michael Ellerman <mpe@ellerman.id.au>, "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>, Russell Currey <ruscur@russell.cc>, Stephen Rothwell <sfr@ozlabs.org>, Heiko Carstens <heiko.carstens@de.ibm.com>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, "linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>
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[ Purple is a nice shade on the bike shed. ;-) ]

On Tue, 14 May 2019 11:02:17 +0200
Geert Uytterhoeven <geert@linux-m68k.org> wrote:

> On Tue, May 14, 2019 at 10:29 AM David Laight <David.Laight@aculab.com> wrote:
> > > And I like Steven's "(fault)" idea.
> > > How about this:
> > >
> > >       if ptr < PAGE_SIZE              -> "(null)"
> > >       if IS_ERR_VALUE(ptr)            -> "(fault)"
> > >
> > >       -ss  
> >
> > Or:
> >         if (ptr < PAGE_SIZE)
> >                 return ptr ? "(null+)" : "(null)";

Hmm, that is useful.

> >         if IS_ERR_VALUE(ptr)
> >                 return "(errno)"  

I still prefer "(fault)" as is pretty much all I would expect from a
pointer dereference, even if it is just bad parsing of, say, a parsing
an MAC address. "fault" is generic enough. "errno" will be confusing,
because that's normally a variable not a output.

> 
> Do we care about the value? "(-E%u)"?

That too could be confusing. What would (-E22) be considered by a user
doing an sprintf() on some string. I know that would confuse me, or I
would think that it was what the %pX displayed, and wonder why it
displayed it that way. Whereas "(fault)" is quite obvious for any %p
use case.

-- Steve