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

[Jacek Anaszewski]

Hi Greg,

Akinobu seems to have addressed all issues that have been
raised regarding this patch. I'd be happy to have your ack before
applying it.

Best regards,
Jacek Anaszewski

On 9/13/19 5:03 PM, Akinobu Mita wrote:
> 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@xxxxxxxxxxxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> Cc: Jacek Anaszewski <jacek.anaszewski@xxxxxxxxx>
> Cc: Pavel Machek <pavel@xxxxxx>
> Cc: Dan Murphy <dmurphy@xxxxxx>
> Acked-by: Pavel Machek <pavel@xxxxxx>
> Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
> ---
>  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);
>