linux-kernel - Re: [PATCH] lib/vsprintf.c: update documentation

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Date:	Fri, 02 Oct 2015 15:47:19 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>
Cc:	Martin Kletzander <mkletzan@...hat.com>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/vsprintf.c: update documentation

On Fri, 2015-10-02 at 14:28 +0200, Rasmus Villemoes wrote:
> %n is no longer just ignored; it results in early return from
> vsnprintf. Also add a request to add test cases for future %p
> extensions.

Nice!

Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
> applies on top of
> lib-documentation-synchronize-%p-formatting-documentation.patch and
> its -fix.
> 
>  Documentation/printk-formats.txt | 12 ++++++------
>  lib/vsprintf.c                   |  7 ++++---
>  2 files changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/printk-formats.txt b/Documentation/printk
> -formats.txt
> index 9b8d7f746b1a..b784c270105f 100644
> --- a/Documentation/printk-formats.txt
> +++ b/Documentation/printk-formats.txt
> @@ -23,6 +23,10 @@ Example:
>  
>  Reminder: sizeof() result is of type size_t.
>  
> +The kernel's printf does not support %n. For obvious reasons, 
> floating
> +point formats (%e, %f, %g, %a) are also not recognized. Use of any
> +unsupported specifier or length qualifier results in a WARN and 
> early
> +return from vsnprintf.
>  
>  Raw pointer value SHOULD be printed with %p. The kernel supports
>  the following extended format specifiers for pointer types:
> @@ -305,13 +309,9 @@ Command from struct task_struct
>  
>  	Passed by reference.
>  
> -Ignored argument:
> +If you add other %p extensions, please extend lib/test_printf.c with
> +one or more test cases, if at all feasible.
>  
> -	%n	%n
> -
> -	The argument passed will be ignored.  In other words, 
> literal "%n" will
> -	be in the output and the argument will be considered for 
> next format
> -	specifier.
>  
>  Thank you for your cooperation and attention.
>  
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 5028b044d0e5..488ee489279a 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1448,7 +1448,6 @@ int kptr_restrict __read_mostly;
>   * - 'Cn' For a clock, it prints the name (Common Clock Framework) 
> or address
>   *        (legacy clock framework) of the clock
>   * - 'Cr' For a clock, it prints the current rate of the clock
> - * - 'n' For ignored argument
>   *
>   * ** Please update also Documentation/printk-formats.txt when 
> making changes **
>   *
> @@ -1814,8 +1813,10 @@ qualifier:
>   * @fmt: The format string to use
>   * @args: Arguments for the format string
>   *
> - * This function follows C99 vsnprintf, but has some extensions:
> - * %n is ignored
> + * This function generally follows C99 vsnprintf, but has some
> + * extensions and a few limitations:
> + *
> + * %n is unsupported
>   * %p* is handled by pointer()
>   *
>   * See pointer() or Documentation/printk-formats.txt for more

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy
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