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

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 <>
Reviewed-by: default avatarMartin Kletzander <>
Reviewed-by: default avatarAndy Shevchenko <>
Cc: Jonathan Corbet <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 317dc34a
......@@ -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
Thank you for your cooperation and attention.
......@@ -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
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