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: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 6 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.