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From:   Heiner Kallweit <hkallweit1@gmail.com>
To:     Jason Baron <jbaron@akamai.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <f527618e-54f2-c2fb-e267-8065ac34e462@gmail.com>
Subject: [PATCH 1/2] dyndbg: add pr_debug return value if dynamic debugging is
 enabled
Message-ID: <c552470c-f963-aff8-9b51-af70a664a590@gmail.com>
Date:   Mon, 3 May 2021 21:39:24 +0200
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If a pr_cont() follows a pr_debug() then it must not print something if
the the pr_debug() output is suppressed. We can use the pr_debug() return
value as criteria, however this fails in case dynamic debugging is enabled
because dynamic_pr_debug() has no return value. So let's add this missing
feature.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
 include/linux/dynamic_debug.h | 14 +++++++++++---
 lib/dynamic_debug.c           |  7 +++++--
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index a57ee7534..1de271d1a 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -57,7 +57,7 @@ int ddebug_add_module(struct _ddebug *tab, unsigned int n,
 				const char *modname);
 extern int ddebug_remove_module(const char *mod_name);
 extern __printf(2, 3)
-void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...);
+int __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...);
 
 extern int ddebug_dyndbg_module_param_cb(char *param, char *val,
 					const char *modname);
@@ -123,6 +123,14 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 
 #endif /* CONFIG_JUMP_LABEL */
 
+#define __dynamic_func_call_pr_debug(id, fmt, ...) ({		\
+	DEFINE_DYNAMIC_DEBUG_METADATA(id, fmt);			\
+	int ret = 0;						\
+	if (DYNAMIC_DEBUG_BRANCH(id))				\
+		ret = __dynamic_pr_debug(&id, __VA_ARGS__);	\
+	ret;							\
+})
+
 #define __dynamic_func_call(id, fmt, func, ...) do {	\
 	DEFINE_DYNAMIC_DEBUG_METADATA(id, fmt);		\
 	if (DYNAMIC_DEBUG_BRANCH(id))			\
@@ -154,8 +162,8 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 	__dynamic_func_call_no_desc(__UNIQUE_ID(ddebug), fmt, func, ##__VA_ARGS__)
 
 #define dynamic_pr_debug(fmt, ...)				\
-	_dynamic_func_call(fmt,	__dynamic_pr_debug,		\
-			   pr_fmt(fmt), ##__VA_ARGS__)
+	__dynamic_func_call_pr_debug(__UNIQUE_ID(ddebug), fmt,	\
+				     pr_fmt(fmt), ##__VA_ARGS__)
 
 #define dynamic_dev_dbg(dev, fmt, ...)				\
 	_dynamic_func_call(fmt,__dynamic_dev_dbg, 		\
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index c70d6347a..f7a771c06 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -618,11 +618,12 @@ static char *dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
 	return buf;
 }
 
-void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...)
+int __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...)
 {
 	va_list args;
 	struct va_format vaf;
 	char buf[PREFIX_SIZE];
+	int ret;
 
 	BUG_ON(!descriptor);
 	BUG_ON(!fmt);
@@ -632,9 +633,11 @@ void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...)
 	vaf.fmt = fmt;
 	vaf.va = &args;
 
-	printk(KERN_DEBUG "%s%pV", dynamic_emit_prefix(descriptor, buf), &vaf);
+	ret = printk(KERN_DEBUG "%s%pV", dynamic_emit_prefix(descriptor, buf), &vaf);
 
 	va_end(args);
+
+	return ret;
 }
 EXPORT_SYMBOL(__dynamic_pr_debug);
 
-- 
2.31.1