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>

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 9b8d7f746b1a6ad3cdfaf2d2c93675ab69f4f12c..b784c270105f40e8320cd388cb9a8ef1e2d463f4 100644 (file)
--- 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 7848d53a51341607e8b2cc0777cf547b586230a1..f9cee8e1233c0fe0f626fe2680ca4b9ff9d3153e 100644 (file)
--- 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