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

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Date:	Fri,  2 Oct 2015 14:28:06 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>
Cc:	Martin Kletzander <mkletzan@...hat.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] 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@...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
-- 
2.1.3

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