leds: remove PAGE_SIZE limit of /sys/class/leds/<led>/trigger

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.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Dan Murphy <dmurphy@ti.com>A
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

1 files changed, 68 insertions, 22 deletions

diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index 23963e5cb5d6..79e30d2cb7a5 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 +67,82 @@ unlock:
 	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(3, 4)
+static int led_trigger_snprintf(char *buf, ssize_t size, const char *fmt, ...)
+{
+	va_list args;
+	int i;
+
+	va_start(args, fmt);
+	if (size <= 0)
+		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,
+			      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, "%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,
+					    " %s%s%s", hit ? "[" : "",
+					    trig->name, hit ? "]" : "");
+	}
+
+	len += led_trigger_snprintf(buf + len, size - len, "\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] ");
-	else
-		len += scnprintf(buf+len, PAGE_SIZE - len, "none ");
-
-	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);
+	len = led_trigger_format(NULL, 0, led_cdev);
+	data = kvmalloc(len + 1, GFP_KERNEL);
+	if (!data) {
+		up_read(&led_cdev->trigger_lock);
+		up_read(&triggers_list_lock);
+		return -ENOMEM;
 	}
+	len = led_trigger_format(data, len + 1, led_cdev);
+
 	up_read(&led_cdev->trigger_lock);
 	up_read(&triggers_list_lock);
 
-	len += scnprintf(len+buf, PAGE_SIZE - len, "\n");
+	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)