linux-kernel - [PATCH] printf: Emit "SUCCESS" if NULL is passed for %pe

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Date:   Fri, 30 Sep 2022 13:10:50 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de
Subject: [PATCH] printf: Emit "SUCCESS" if NULL is passed for %pe

For code that emits a string representing a usual return value it's
convenient to have a 0 result in a string representation of success
instead of "00000000".

A usecase is tracing where the return value of a callback is emitted,
see
https://lore.kernel.org/linux-pwm/20220916151506.298488-2-u.kleine-koenig@pengutronix.de
for an example.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
---
 lib/errname.c  | 1 +
 lib/vsprintf.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/errname.c b/lib/errname.c
index 05cbf731545f..2fd430f25059 100644
--- a/lib/errname.c
+++ b/lib/errname.c
@@ -15,6 +15,7 @@
  */
 #define E(err) [err + BUILD_BUG_ON_ZERO(err <= 0 || err > 300)] = "-" #err
 static const char *names_0[] = {
+	[0] = "SUCCESS",
 	E(E2BIG),
 	E(EACCES),
 	E(EADDRINUSE),
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 3c1853a9d1c0..2a27218bab48 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2448,7 +2448,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 		return pointer_string(buf, end, ptr, spec);
 	case 'e':
 		/* %pe with a non-ERR_PTR gets treated as plain %p */
-		if (!IS_ERR(ptr))
+		if (!IS_ERR_OR_NULL(ptr))
 			return default_pointer(buf, end, ptr, spec);
 		return err_ptr(buf, end, ptr, spec);
 	case 'u':
-- 
2.30.2