[PATCH v2 1/1] leds: remove PAGE_SIZE limit of /sys/class/leds/<led>/trigger

[Akinobu Mita <akinobu.mita@gmail.com>]

Reading /sys/class/leds/<led>/trigger returns all available LED triggers.
However, the size of this file is limited to PAGE_SIZE because of the
limitation for sysfs attribute.

Enabling LED CPU trigger on systems with thousands of CPUs easily hits
PAGE_SIZE limit, and makes it impossible to see all available LED triggers
and which trigger is currently activated.

We work around it here by converting /sys/class/leds/<led>/trigger to
binary attribute, which is not limited by length. This is _not_ good
design, do not copy it.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Dan Murphy <dmurphy@ti.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 drivers/leds/led-class.c    |  8 ++--
 drivers/leds/led-triggers.c | 90 ++++++++++++++++++++++++++++++++++-----------
 drivers/leds/leds.h         |  6 +++
 include/linux/leds.h        |  5 ---
 4 files changed, 79 insertions(+), 30 deletions(-)

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 4793e77..8b5a1d1 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -73,13 +73,13 @@ static ssize_t max_brightness_show(struct device *dev,
 static DEVICE_ATTR_RO(max_brightness);
 
 #ifdef CONFIG_LEDS_TRIGGERS
-static DEVICE_ATTR(trigger, 0644, led_trigger_show, led_trigger_store);
-static struct attribute *led_trigger_attrs[] = {
-	&dev_attr_trigger.attr,
+static BIN_ATTR(trigger, 0644, led_trigger_read, led_trigger_write, 0);
+static struct bin_attribute *led_trigger_bin_attrs[] = {
+	&bin_attr_trigger,
 	NULL,
 };
 static const struct attribute_group led_trigger_group = {
-	.attrs = led_trigger_attrs,
+	.bin_attrs = led_trigger_bin_attrs,
 };
 #endif
 
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index 8d11a5e..ed5a311 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -16,6 +16,7 @@
 #include <linux/rwsem.h>
 #include <linux/leds.h>
 #include <linux/slab.h>
+#include <linux/mm.h>
 #include "leds.h"
 
 /*
@@ -26,9 +27,11 @@ LIST_HEAD(trigger_list);
 
  /* Used by LED Class */
 
-ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
-		const char *buf, size_t count)
+ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
+			  struct bin_attribute *bin_attr, char *buf,
+			  loff_t pos, size_t count)
 {
+	struct device *dev = kobj_to_dev(kobj);
 	struct led_classdev *led_cdev = dev_get_drvdata(dev);
 	struct led_trigger *trig;
 	int ret = count;
@@ -64,39 +67,84 @@ ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
 	mutex_unlock(&led_cdev->led_access);
 	return ret;
 }
-EXPORT_SYMBOL_GPL(led_trigger_store);
+EXPORT_SYMBOL_GPL(led_trigger_write);
 
-ssize_t led_trigger_show(struct device *dev, struct device_attribute *attr,
-		char *buf)
+__printf(4, 5)
+static int led_trigger_snprintf(char *buf, size_t size, bool query,
+				const char *fmt, ...)
+{
+	va_list args;
+	int i;
+
+	va_start(args, fmt);
+	if (query)
+		i = vsnprintf(NULL, 0, fmt, args);
+	else
+		i = vscnprintf(buf, size, fmt, args);
+	va_end(args);
+
+	return i;
+}
+
+static int led_trigger_format(char *buf, size_t size, bool query,
+			      struct led_classdev *led_cdev)
 {
-	struct led_classdev *led_cdev = dev_get_drvdata(dev);
 	struct led_trigger *trig;
-	int len = 0;
+	int len = led_trigger_snprintf(buf, size, query, "%s",
+				       led_cdev->trigger ? "none" : "[none]");
+
+	list_for_each_entry(trig, &trigger_list, next_trig) {
+		bool hit = led_cdev->trigger &&
+			!strcmp(led_cdev->trigger->name, trig->name);
+
+		len += led_trigger_snprintf(buf + len, size - len, query,
+					    " %s%s%s", hit ? "[" : "",
+					    trig->name, hit ? "]" : "");
+	}
+
+	len += led_trigger_snprintf(buf + len, size - len, query, "\n");
+
+	return len;
+}
+
+/*
+ * It was stupid to create 10000 cpu triggers, but we are stuck with it now.
+ * Don't make that mistake again. We work around it here by creating binary
+ * attribute, which is not limited by length. This is _not_ good design, do not
+ * copy it.
+ */
+ssize_t led_trigger_read(struct file *filp, struct kobject *kobj,
+			struct bin_attribute *attr, char *buf,
+			loff_t pos, size_t count)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct led_classdev *led_cdev = dev_get_drvdata(dev);
+	void *data;
+	int len;
 
 	down_read(&triggers_list_lock);
 	down_read(&led_cdev->trigger_lock);
 
-	if (!led_cdev->trigger)
-		len += scnprintf(buf+len, PAGE_SIZE - len, "[none] ");
+	len = led_trigger_format(NULL, 0, true, led_cdev);
+	data = kvmalloc(len + 1, GFP_KERNEL);
+	if (data)
+		len = led_trigger_format(data, len + 1, false, led_cdev);
 	else
-		len += scnprintf(buf+len, PAGE_SIZE - len, "none ");
+		len = -ENOMEM;
 
-	list_for_each_entry(trig, &trigger_list, next_trig) {
-		if (led_cdev->trigger && !strcmp(led_cdev->trigger->name,
-							trig->name))
-			len += scnprintf(buf+len, PAGE_SIZE - len, "[%s] ",
-					 trig->name);
-		else
-			len += scnprintf(buf+len, PAGE_SIZE - len, "%s ",
-					 trig->name);
-	}
 	up_read(&led_cdev->trigger_lock);
 	up_read(&triggers_list_lock);
 
-	len += scnprintf(len+buf, PAGE_SIZE - len, "\n");
+	if (len < 0)
+		return len;
+
+	len = memory_read_from_buffer(buf, count, &pos, data, len);
+
+	kvfree(data);
+
 	return len;
 }
-EXPORT_SYMBOL_GPL(led_trigger_show);
+EXPORT_SYMBOL_GPL(led_trigger_read);
 
 /* Caller must ensure led_cdev->trigger_lock held */
 int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
diff --git a/drivers/leds/leds.h b/drivers/leds/leds.h
index 47b2294..a0ee33c 100644
--- a/drivers/leds/leds.h
+++ b/drivers/leds/leds.h
@@ -23,6 +23,12 @@ void led_set_brightness_nopm(struct led_classdev *led_cdev,
 				enum led_brightness value);
 void led_set_brightness_nosleep(struct led_classdev *led_cdev,
 				enum led_brightness value);
+ssize_t led_trigger_read(struct file *filp, struct kobject *kobj,
+			struct bin_attribute *attr, char *buf,
+			loff_t pos, size_t count);
+ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
+			struct bin_attribute *bin_attr, char *buf,
+			loff_t pos, size_t count);
 
 extern struct rw_semaphore leds_list_lock;
 extern struct list_head leds_list;
diff --git a/include/linux/leds.h b/include/linux/leds.h
index fd2eb7c..33ae825 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -290,11 +290,6 @@ struct led_trigger {
 #define led_trigger_get_led(dev)	((struct led_classdev *)dev_get_drvdata((dev)))
 #define led_trigger_get_drvdata(dev)	(led_get_trigger_data(led_trigger_get_led(dev)))
 
-ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
-			const char *buf, size_t count);
-ssize_t led_trigger_show(struct device *dev, struct device_attribute *attr,
-			char *buf);
-
 /* Registration functions for complex triggers */
 extern int led_trigger_register(struct led_trigger *trigger);
 extern void led_trigger_unregister(struct led_trigger *trigger);
-- 
2.7.4