PM / sleep: Do not print debug messages by default

Debug messages from the system suspend/hibernation infrastructure can
fill up the entire kernel log buffer in some cases and anyway they
are only useful for debugging.  They depend on CONFIG_PM_DEBUG, but
that is set as a rule as some generally useful diagnostic facilities
depend on it too.

For this reason, avoid printing those messages by default, but make
it possible to turn them on as needed with the help of a new sysfs
attribute under /sys/power/.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/kernel/power/main.c b/kernel/power/main.c
index 42bd800..5ce0090 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -361,6 +361,57 @@ static ssize_t pm_wakeup_irq_show(struct kobject *kobj,
 
 power_attr_ro(pm_wakeup_irq);
 
+static bool pm_debug_messages_on __read_mostly;
+
+static ssize_t pm_debug_messages_show(struct kobject *kobj,
+				      struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%d\n", pm_debug_messages_on);
+}
+
+static ssize_t pm_debug_messages_store(struct kobject *kobj,
+				       struct kobj_attribute *attr,
+				       const char *buf, size_t n)
+{
+	unsigned long val;
+
+	if (kstrtoul(buf, 10, &val))
+		return -EINVAL;
+
+	if (val > 1)
+		return -EINVAL;
+
+	pm_debug_messages_on = !!val;
+	return n;
+}
+
+power_attr(pm_debug_messages);
+
+/**
+ * pm_pr_dbg - Print a suspend debug message to the kernel log.
+ * @fmt: Message format.
+ *
+ * The message will be emitted if enabled through the pm_debug_messages
+ * sysfs attribute.
+ */
+void pm_pr_dbg(const char *fmt, ...)
+{
+	struct va_format vaf;
+	va_list args;
+
+	if (!pm_debug_messages_on)
+		return;
+
+	va_start(args, fmt);
+
+	vaf.fmt = fmt;
+	vaf.va = &args;
+
+	printk(KERN_DEBUG "PM: %pV", &vaf);
+
+	va_end(args);
+}
+
 #else /* !CONFIG_PM_SLEEP_DEBUG */
 static inline void pm_print_times_init(void) {}
 #endif /* CONFIG_PM_SLEEP_DEBUG */
@@ -697,6 +748,7 @@ static struct attribute * g[] = {
 #ifdef CONFIG_PM_SLEEP_DEBUG
 	&pm_print_times_attr.attr,
 	&pm_wakeup_irq_attr.attr,
+	&pm_debug_messages_attr.attr,
 #endif
 #endif
 #ifdef CONFIG_FREEZER