[PATCH v6 4/4] printk: index: Add indexing support to dev_printk

[Chris Down]

While for most kinds of issues we have counters, tracepoints, or metrics
with a stable interface which can reliably be used to indicate issues,
in order to react to production issues quickly we sometimes need to work
with the interface which most kernel developers naturally use when
developing: printk, and printk-esques like dev_printk.

dev_printk is by far the most likely custom subsystem printk to benefit
from the printk indexing infrastructure, since niche device issues
brought about by production changes, firmware upgrades, and the like are
one of the most common things that we need printk infrastructure's
assistance to monitor.

Often these errors were never expected to practically manifest in
reality, and exhibit in code without extensive (or any) metrics present.
As such, there are typically very few options for issue detection
available to those with large fleets at the time the incident happens,
and we thus benefit strongly from monitoring netconsole in these
instances.

As such, add the infrastructure for dev_printk to be indexed in the
printk index. Even on a minimal kernel config, the coverage of the base
kernel's printk index is significantly improved:

Before:

    [root@ktst ~]# wc -l /sys/kernel/debug/printk/index/vmlinux
    4497 /sys/kernel/debug/printk/index/vmlinux

After:

    [root@ktst ~]# wc -l /sys/kernel/debug/printk/index/vmlinux
    5573 /sys/kernel/debug/printk/index/vmlinux

In terms of implementation, in order to trivially disambiguate them,
dev_printk is now a macro which wraps _dev_printk. If preferred, it's
also possible to have the macro and function have the same name.

Signed-off-by: Chris Down <chris@xxxxxxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
---
 drivers/base/core.c        |  6 ++--
 include/linux/dev_printk.h | 63 ++++++++++++++++++++++++++++----------
 2 files changed, 49 insertions(+), 20 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 60c5f5ea0268..78b8297e7f2b 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -4547,8 +4547,8 @@ static void __dev_printk(const char *level, const struct device *dev,
 		printk("%s(NULL device *): %pV", level, vaf);
 }
 
-void dev_printk(const char *level, const struct device *dev,
-		const char *fmt, ...)
+void _dev_printk(const char *level, const struct device *dev,
+		 const char *fmt, ...)
 {
 	struct va_format vaf;
 	va_list args;
@@ -4562,7 +4562,7 @@ void dev_printk(const char *level, const struct device *dev,
 
 	va_end(args);
 }
-EXPORT_SYMBOL(dev_printk);
+EXPORT_SYMBOL(_dev_printk);
 
 #define define_dev_printk_level(func, kern_level)		\
 void func(const struct device *dev, const char *fmt, ...)	\
diff --git a/include/linux/dev_printk.h b/include/linux/dev_printk.h
index 6f009559ee54..202c6a9ea7eb 100644
--- a/include/linux/dev_printk.h
+++ b/include/linux/dev_printk.h
@@ -38,8 +38,8 @@ __printf(3, 4) __cold
 int dev_printk_emit(int level, const struct device *dev, const char *fmt, ...);
 
 __printf(3, 4) __cold
-void dev_printk(const char *level, const struct device *dev,
-		const char *fmt, ...);
+void _dev_printk(const char *level, const struct device *dev,
+		 const char *fmt, ...);
 __printf(2, 3) __cold
 void _dev_emerg(const struct device *dev, const char *fmt, ...);
 __printf(2, 3) __cold
@@ -69,7 +69,7 @@ static inline void __dev_printk(const char *level, const struct device *dev,
 				struct va_format *vaf)
 {}
 static inline __printf(3, 4)
-void dev_printk(const char *level, const struct device *dev,
+void _dev_printk(const char *level, const struct device *dev,
 		 const char *fmt, ...)
 {}
 
@@ -97,25 +97,54 @@ void _dev_info(const struct device *dev, const char *fmt, ...)
 
 #endif
 
+/*
+ * Some callsites directly call dev_printk rather than going through the
+ * dev_<level> infrastructure, so we need to emit here as well as inside those
+ * level-specific macros. Only one index entry will be produced, either way,
+ * since dev_printk's `fmt` isn't known at compile time if going through the
+ * dev_<level> macros.
+ */
+#define dev_printk(level, dev, fmt, ...) ({			\
+	dev_printk_index_emit(level, fmt);			\
+	_dev_printk(level, dev, fmt, ##__VA_ARGS__);		\
+})
+
 /*
  * #defines for all the dev_<level> macros to prefix with whatever
  * possible use of #define dev_fmt(fmt) ...
  */
 
-#define dev_emerg(dev, fmt, ...)					\
-	_dev_emerg(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_crit(dev, fmt, ...)						\
-	_dev_crit(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_alert(dev, fmt, ...)					\
-	_dev_alert(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_err(dev, fmt, ...)						\
-	_dev_err(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_warn(dev, fmt, ...)						\
-	_dev_warn(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_notice(dev, fmt, ...)					\
-	_dev_notice(dev, dev_fmt(fmt), ##__VA_ARGS__)
-#define dev_info(dev, fmt, ...)						\
-	_dev_info(dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_printk_index_emit(level, fmt)				\
+	printk_index_subsys_emit("%s %s: ", "", level, fmt)
+
+#define dev_emerg(dev, fmt, ...) ({					\
+	dev_printk_index_emit(KERN_EMERG, dev_fmt(fmt));		\
+	_dev_emerg(dev, dev_fmt(fmt), ##__VA_ARGS__);			\
+})
+#define dev_crit(dev, fmt, ...) ({					\
+	dev_printk_index_emit(KERN_CRIT, dev_fmt(fmt));			\
+	_dev_crit(dev, dev_fmt(fmt), ##__VA_ARGS__);			\
+})
+#define dev_alert(dev, fmt, ...) ({					\
+	dev_printk_index_emit(KERN_ALERT, dev_fmt(fmt));		\
+	_dev_alert(dev, dev_fmt(fmt), ##__VA_ARGS__);			\
+})
+#define dev_err(dev, fmt, ...) ({					\
+	dev_printk_index_emit(KERN_ERR, dev_fmt(fmt));			\
+	_dev_err(dev, dev_fmt(fmt), ##__VA_ARGS__);			\
+})
+#define dev_warn(dev, fmt, ...) ({					\
+	dev_printk_index_emit(KERN_WARNING, dev_fmt(fmt));		\
+	_dev_warn(dev, dev_fmt(fmt), ##__VA_ARGS__);			\
+})
+#define dev_notice(dev, fmt, ...) ({					\
+	dev_printk_index_emit(KERN_NOTICE, dev_fmt(fmt));		\
+	_dev_notice(dev, dev_fmt(fmt), ##__VA_ARGS__);			\
+})
+#define dev_info(dev, fmt, ...) ({					\
+	dev_printk_index_emit(KERN_INFO, dev_fmt(fmt));			\
+	_dev_info(dev, dev_fmt(fmt), ##__VA_ARGS__);			\
+})
 
 #if defined(CONFIG_DYNAMIC_DEBUG) || \
 	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
-- 
2.31.1