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Commit d7ec9a05 authored by Rasmus Villemoes's avatar Rasmus Villemoes Committed by Linus Torvalds
Browse files

lib/vsprintf.c: update documentation 



%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.

Signed-off-by: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: default avatarMartin Kletzander <mkletzan@redhat.com>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 317dc34a

Documentation/printk-formats.txt

+6 −6
Original line number Diff line number Diff line
@@ -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.

lib/vsprintf.c

+4 −3
Original line number Diff line number Diff line
@@ -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 @@ int format_decode(const char *fmt, struct printf_spec *spec) 
 * @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