[PATCH v7 5/5] printk: index: Add indexing support to dev_printk

[Chris Down <chris@chrisdown.name>]

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.

Signed-off-by: Chris Down <chris@chrisdown.name>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 drivers/base/core.c        |  6 ++--
 include/linux/dev_printk.h | 66 ++++++++++++++++++++++++++++----------
 2 files changed, 52 insertions(+), 20 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index b8a8c96dca58..31a24b4e27cd 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -4579,8 +4579,8 @@ 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;
@@ -4594,7 +4594,7 @@ 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..8da7452cae3f 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 +97,57 @@ void _dev_info(const struct device *dev, const char *fmt, ...)
 
 #endif
 
+/*
+ * Need to take variadic arguments even though we don't use them, as dev_fmt()
+ * may only just have been expanded and may result in multiple arguments.
+ */
+#define dev_printk_index_emit(level, fmt, ...) \
+	printk_index_subsys_emit("%s %s: ", level, fmt)
+
+#define dev_printk_index_wrap(_p_func, level, dev, fmt, ...)		\
+	({								\
+		dev_printk_index_emit(level, fmt);			\
+		_p_func(dev, fmt, ##__VA_ARGS__);			\
+	})
+
+/*
+ * 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.
+ *
+ * dev_fmt() isn't called for dev_printk when used directly, as it's used by
+ * the dev_<level> macros internally which already have dev_fmt() processed.
+ *
+ * We also can't use dev_printk_index_wrap directly, because we have a separate
+ * level to process.
+ */
+#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_emerg(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_emerg, KERN_EMERG, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_crit(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_crit, KERN_CRIT, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_alert(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_alert, KERN_ALERT, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_err(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_err, KERN_ERR, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_warn(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_warn, KERN_WARNING, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_notice(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_notice, KERN_NOTICE, dev, dev_fmt(fmt), ##__VA_ARGS__)
+#define dev_info(dev, fmt, ...) \
+	dev_printk_index_wrap(_dev_info, KERN_INFO, dev, dev_fmt(fmt), ##__VA_ARGS__)
 
 #if defined(CONFIG_DYNAMIC_DEBUG) || \
 	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
-- 
2.31.1