[PATCH] lib/vsprintf.c: update documentation

Rasmus Villemoes
2015-10-02T12:28:27Z

%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>
---
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