linux-kernel - Re: [PATCH v7 07/10] vsprintf: Consolidate handling of unknown pointer specifiers

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Message-ID: <20190626104633.arpobvevpxnkrt5k@pathway.suse.cz>
Date:   Wed, 26 Jun 2019 12:46:33 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Tobin C . Harding" <me@...in.cc>, Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 07/10] vsprintf: Consolidate handling of unknown
 pointer specifiers

On Tue 2019-06-25 12:59:57, Geert Uytterhoeven wrote:
> Hi Petr,
> 
> On Wed, Apr 17, 2019 at 1:56 PM Petr Mladek <pmladek@...e.com> wrote:
> > There are few printk formats that make sense only with two or more
> > specifiers. Also some specifiers make sense only when a kernel feature
> > is enabled.
> >
> > The handling of unknown specifiers is inconsistent and not helpful.
> > Using WARN() looks like an overkill for this type of error. pr_warn()
> > is not good either. It would by handled via printk_safe buffer and
> > it might be hard to match it with the problematic string.
> >
> > A reasonable compromise seems to be writing the unknown format specifier
> > into the original string with a question mark, for example (%pC?).
> > It should be self-explaining enough. Note that it is in brackets
> > to follow the (null) style.
> >
> > Note that it introduces a warning about that test_hashed() function
> > is unused. It is going to be used again by a later patch.
> >
> > Signed-off-by: Petr Mladek <pmladek@...e.com>
> 
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -1706,7 +1712,7 @@ char *clock(char *buf, char *end, struct clk *clk, struct printf_spec spec,
> >  #ifdef CONFIG_COMMON_CLK
> >                 return string(buf, end, __clk_get_name(clk), spec);
> >  #else
> > -               return ptr_to_id(buf, end, clk, spec);
> > +               return string_nocheck(buf, end, "(%pC?)", spec);
> 
> What's the reason behind this change? This is not an error case,
> but for printing the clock pointer as a distinguishable ID when using
> the legacy clock framework, which does not store names with clocks.

You are right. We should put back ptr_to_id() there.

Would you like to send a patch?

Best Regards,
Petr