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 <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Jacek Anaszewski <[email protected]>
Cc: Pavel Machek <[email protected]>
Cc: Dan Murphy <[email protected]>
Acked-by: Pavel Machek <[email protected]>
Signed-off-by: Akinobu Mita <[email protected]>
---
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
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 <[email protected]>
> Cc: "Rafael J. Wysocki" <[email protected]>
> Cc: Jacek Anaszewski <[email protected]>
> Cc: Pavel Machek <[email protected]>
> Cc: Dan Murphy <[email protected]>
> Acked-by: Pavel Machek <[email protected]>
> Signed-off-by: Akinobu Mita <[email protected]>
> ---
> 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);
>
On Tue, Sep 24, 2019 at 11:30:08PM +0200, Jacek Anaszewski wrote:
> 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.
You have to wait until after -rc1 is out before doing anything, so
there's no rush :)
I'll go review it now...
greg k-h
On Sat, Sep 14, 2019 at 12:03:24AM +0900, 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 <[email protected]>
> Cc: "Rafael J. Wysocki" <[email protected]>
> Cc: Jacek Anaszewski <[email protected]>
> Cc: Pavel Machek <[email protected]>
> Cc: Dan Murphy <[email protected]>
> Acked-by: Pavel Machek <[email protected]>
> Signed-off-by: Akinobu Mita <[email protected]>
> ---
> 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;
> +}
You only call this in one place, why is it needed like this? The "old"
code open-coded this, what is this helping with here?
And what does "query" mean here? I have no idea how that variable
matters, or what it does. Why not just test if buf is NULL or not if
you don't want to use it?
Ah, you are trying to see how "long" the buffer is going to be. That
makes more sense, but just trigger off of the NULL buffer or not, making
this a bit more "obvious" what you are doing and not tieing two
parameters to each other (meaning one always reflects the other one).
> +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);
Why kvmalloc() and not just kmalloc()? How big is this buffer you are
expecting to have here?
> + 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);
Two locks? Why not 3? 5? How about just 1? :)
>
> - len += scnprintf(len+buf, PAGE_SIZE - len, "\n");
> + if (len < 0)
> + return len;
You just leaked data if led_trigger_format() returned an error :(
Just return -ENOMEM above if !data, which makes this much simpler.
thanks,
greg k-h
2019年9月27日(金) 15:39 Greg Kroah-Hartman <[email protected]>:
>
> On Sat, Sep 14, 2019 at 12:03:24AM +0900, 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 <[email protected]>
> > Cc: "Rafael J. Wysocki" <[email protected]>
> > Cc: Jacek Anaszewski <[email protected]>
> > Cc: Pavel Machek <[email protected]>
> > Cc: Dan Murphy <[email protected]>
> > Acked-by: Pavel Machek <[email protected]>
> > Signed-off-by: Akinobu Mita <[email protected]>
> > ---
> > 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;
> > +}
>
> You only call this in one place, why is it needed like this? The "old"
> code open-coded this, what is this helping with here?
>
> And what does "query" mean here? I have no idea how that variable
> matters, or what it does. Why not just test if buf is NULL or not if
> you don't want to use it?
>
> Ah, you are trying to see how "long" the buffer is going to be. That
> makes more sense, but just trigger off of the NULL buffer or not, making
> this a bit more "obvious" what you are doing and not tieing two
> parameters to each other (meaning one always reflects the other one).
We cannot simply replace the "query" by checking the buffer is NULL or not.
Because led_trigger_snprintf() is repeatedly called by led_trigger_format()
while increasing 'buf' and decreasing 'size' by the return value of
led_trigger_snprintf() every time.
> > +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);
>
> Why kvmalloc() and not just kmalloc()? How big is this buffer you are
> expecting to have here?
The ledtrig-cpu supports upto 9999 cpus. If all these cpus were available,
the buffer size would be 78,890 bytes.
(for i in `seq 0 9999`;do echo -n " cpu$i"; done | wc -c)
The intention of this kvmalloc() allocation is to avoid costly allocation
if possible.
> > + 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);
>
> Two locks? Why not 3? 5? How about just 1? :)
I don't touch these locks in this patch :)
Locking both locks seems to be necessary to prevent someone from changing
trigger_list or led_cdev->trigger.
> >
> > - len += scnprintf(len+buf, PAGE_SIZE - len, "\n");
> > + if (len < 0)
> > + return len;
>
> You just leaked data if led_trigger_format() returned an error :(
>
> Just return -ENOMEM above if !data, which makes this much simpler.
We are holding the two locks, so we need to release them before return.
Which one do you prefer?
...
data = kvmalloc(len + 1, GFP_KERNEL);
if (data)
len = led_trigger_format(data, len + 1, false, led_cdev);
else
len = -ENOMEM;
up_read(&led_cdev->trigger_lock);
up_read(&triggers_list_lock);
if (len < 0)
return len;
vs.
...
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, false, led_cdev);
up_read(&led_cdev->trigger_lock);
up_read(&triggers_list_lock);
Hi!
> > > 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);
> >
> > Why kvmalloc() and not just kmalloc()? How big is this buffer you are
> > expecting to have here?
>
> The ledtrig-cpu supports upto 9999 cpus. If all these cpus were available,
> the buffer size would be 78,890 bytes.
> (for i in `seq 0 9999`;do echo -n " cpu$i"; done | wc -c)
>
> The intention of this kvmalloc() allocation is to avoid costly allocation
> if possible.
Sounds good.
> > > - else
> > > - len += scnprintf(buf+len, PAGE_SIZE - len, "%s ",
> > > - trig->name);
> > > - }
> > > up_read(&led_cdev->trigger_lock);
> > > up_read(&triggers_list_lock);
> >
> > Two locks? Why not 3? 5? How about just 1? :)
>
> I don't touch these locks in this patch :)
Nor should you :-).
> > Just return -ENOMEM above if !data, which makes this much simpler.
>
> We are holding the two locks, so we need to release them before return.
> Which one do you prefer?
>
> ...
> data = kvmalloc(len + 1, GFP_KERNEL);
> if (data)
> len = led_trigger_format(data, len + 1, false, led_cdev);
> else
> len = -ENOMEM;
>
> up_read(&led_cdev->trigger_lock);
> up_read(&triggers_list_lock);
>
> if (len < 0)
> return len;
>
> vs.
>
> ...
> 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, false, led_cdev);
>
> up_read(&led_cdev->trigger_lock);
> up_read(&triggers_list_lock);
Second one is better. Using goto to jump to error path doing cleanups
is also acceptable.
Thanks,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
On Sat, Sep 28, 2019 at 01:47:21AM +0900, Akinobu Mita wrote:
> 2019年9月27日(金) 15:39 Greg Kroah-Hartman <[email protected]>:
> >
> > On Sat, Sep 14, 2019 at 12:03:24AM +0900, 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 <[email protected]>
> > > Cc: "Rafael J. Wysocki" <[email protected]>
> > > Cc: Jacek Anaszewski <[email protected]>
> > > Cc: Pavel Machek <[email protected]>
> > > Cc: Dan Murphy <[email protected]>
> > > Acked-by: Pavel Machek <[email protected]>
> > > Signed-off-by: Akinobu Mita <[email protected]>
> > > ---
> > > 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;
> > > +}
> >
> > You only call this in one place, why is it needed like this? The "old"
> > code open-coded this, what is this helping with here?
> >
> > And what does "query" mean here? I have no idea how that variable
> > matters, or what it does. Why not just test if buf is NULL or not if
> > you don't want to use it?
> >
> > Ah, you are trying to see how "long" the buffer is going to be. That
> > makes more sense, but just trigger off of the NULL buffer or not, making
> > this a bit more "obvious" what you are doing and not tieing two
> > parameters to each other (meaning one always reflects the other one).
>
> We cannot simply replace the "query" by checking the buffer is NULL or not.
> Because led_trigger_snprintf() is repeatedly called by led_trigger_format()
> while increasing 'buf' and decreasing 'size' by the return value of
> led_trigger_snprintf() every time.
Odd, but ok, I'll trust you, this looks like very odd code :(
> > > +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);
> >
> > Why kvmalloc() and not just kmalloc()? How big is this buffer you are
> > expecting to have here?
>
> The ledtrig-cpu supports upto 9999 cpus. If all these cpus were available,
> the buffer size would be 78,890 bytes.
> (for i in `seq 0 9999`;do echo -n " cpu$i"; done | wc -c)
>
> The intention of this kvmalloc() allocation is to avoid costly allocation
> if possible.
Ah, forgot it could get that big.
> > > + 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);
> >
> > Two locks? Why not 3? 5? How about just 1? :)
>
> I don't touch these locks in this patch :)
>
> Locking both locks seems to be necessary to prevent someone from changing
> trigger_list or led_cdev->trigger.
Ok, it just looked odd to me.
> > > - len += scnprintf(len+buf, PAGE_SIZE - len, "\n");
> > > + if (len < 0)
> > > + return len;
> >
> > You just leaked data if led_trigger_format() returned an error :(
> >
> > Just return -ENOMEM above if !data, which makes this much simpler.
>
> We are holding the two locks, so we need to release them before return.
> Which one do you prefer?
>
> ...
> data = kvmalloc(len + 1, GFP_KERNEL);
> if (data)
> len = led_trigger_format(data, len + 1, false, led_cdev);
> else
> len = -ENOMEM;
>
> up_read(&led_cdev->trigger_lock);
> up_read(&triggers_list_lock);
>
> if (len < 0)
> return len;
>
> vs.
>
> ...
> 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, false, led_cdev);
>
> up_read(&led_cdev->trigger_lock);
> up_read(&triggers_list_lock);
I don't care, as long as you do not leak memory I'm happy :)
thanks,
greg k-h
2019年9月28日(土) 2:46 Greg Kroah-Hartman <[email protected]>:
>
> On Sat, Sep 28, 2019 at 01:47:21AM +0900, Akinobu Mita wrote:
> > 2019年9月27日(金) 15:39 Greg Kroah-Hartman <[email protected]>:
> > >
> > > On Sat, Sep 14, 2019 at 12:03:24AM +0900, 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 <[email protected]>
> > > > Cc: "Rafael J. Wysocki" <[email protected]>
> > > > Cc: Jacek Anaszewski <[email protected]>
> > > > Cc: Pavel Machek <[email protected]>
> > > > Cc: Dan Murphy <[email protected]>
> > > > Acked-by: Pavel Machek <[email protected]>
> > > > Signed-off-by: Akinobu Mita <[email protected]>
> > > > ---
> > > > 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;
> > > > +}
> > >
> > > You only call this in one place, why is it needed like this? The "old"
> > > code open-coded this, what is this helping with here?
> > >
> > > And what does "query" mean here? I have no idea how that variable
> > > matters, or what it does. Why not just test if buf is NULL or not if
> > > you don't want to use it?
> > >
> > > Ah, you are trying to see how "long" the buffer is going to be. That
> > > makes more sense, but just trigger off of the NULL buffer or not, making
> > > this a bit more "obvious" what you are doing and not tieing two
> > > parameters to each other (meaning one always reflects the other one).
> >
> > We cannot simply replace the "query" by checking the buffer is NULL or not.
> > Because led_trigger_snprintf() is repeatedly called by led_trigger_format()
> > while increasing 'buf' and decreasing 'size' by the return value of
> > led_trigger_snprintf() every time.
>
> Odd, but ok, I'll trust you, this looks like very odd code :(
We can remove the "query" by checking if "size" is less than or equal to
zero in led_trigger_snprintf(), instead of checking "buf".
Because the "size" keeps decreasing every time led_trigger_snprintf() is
called by led_trigger_format().