[PATCH] leds: remove PAGE_SIZE limit of /sys/class/leds//trigger

Akinobu Mita
2019-09-12T14:40:21Z

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