Re: [PATCH/RFC v5 2/4] leds: implement sysfs interface locking mechanism
From: Bryan Wu
Date: Thu Sep 11 2014 - 21:11:42 EST
On Wed, Aug 20, 2014 at 6:41 AM, Jacek Anaszewski
<j.anaszewski@xxxxxxxxxxx> wrote:
> Add a mechanism for locking LED subsystem sysfs interface.
> This patch prepares ground for addition of LED Flash Class
> extension, whose API will be integrated with V4L2 Flash API.
> Such a fusion enforces introducing a locking scheme, which
> will secure consistent access to the LED Flash Class device.
>
> The mechanism being introduced allows for disabling LED
> subsystem sysfs interface by calling led_sysfs_lock function
> and enabling it by calling led_sysfs_unlock. The functions
> alter the LED_SYSFS_LOCK flag state and must be called
> under mutex lock. The state of the lock is checked with use
> of led_sysfs_is_locked function. Such a design allows for
> providing immediate feedback to the user space on whether
> the LED Flash Class device is available or is under V4L2 Flash
> sub-device control.
>
> Signed-off-by: Jacek Anaszewski <j.anaszewski@xxxxxxxxxxx>
> Acked-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
> Cc: Bryan Wu <cooloney@xxxxxxxxx>
> Cc: Richard Purdie <rpurdie@xxxxxxxxx>
> ---
> drivers/leds/led-class.c | 23 ++++++++++++++++++++---
> drivers/leds/led-core.c | 18 ++++++++++++++++++
> drivers/leds/led-triggers.c | 15 ++++++++++++---
> include/linux/leds.h | 32 ++++++++++++++++++++++++++++++++
> 4 files changed, 82 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> index 6f82a76..0bc0ba9 100644
> --- a/drivers/leds/led-class.c
> +++ b/drivers/leds/led-class.c
> @@ -39,17 +39,31 @@ static ssize_t brightness_store(struct device *dev,
> {
> struct led_classdev *led_cdev = dev_get_drvdata(dev);
> unsigned long state;
> - ssize_t ret = -EINVAL;
> + ssize_t ret;
> +
> +#ifdef CONFIG_V4L2_FLASH_LED_CLASS
Can we remove this #ifdef? Following code looks good to the common LED class.
> + mutex_lock(&led_cdev->led_lock);
Can we choose more meaningful name instead of led_lock here?
Then use led_sysfs_enable() instead of led_sysfs_unlock()
led_sysfs_disable instead of led_sysfs_lock()
led_sysfs_is_disabled instead of led_sysfs_is_locked()
And the flag LED_SYSFS_LOCK -> LED_SYSFS_DISABLE
I was just confused by the name lock and unlock and mutex lock.
The idea looks good to me.
Thanks,
-Bryan
> +
> + if (led_sysfs_is_locked(led_cdev)) {
> + ret = -EBUSY;
> + goto unlock;
> + }
> +#endif
>
> ret = kstrtoul(buf, 10, &state);
> if (ret)
> - return ret;
> + goto unlock;
>
> if (state == LED_OFF)
> led_trigger_remove(led_cdev);
> __led_set_brightness(led_cdev, state);
>
> - return size;
> + ret = size;
> +unlock:
> +#ifdef CONFIG_V4L2_FLASH_LED_CLASS
> + mutex_unlock(&led_cdev->led_lock);
> +#endif
> + return ret;
> }
> static DEVICE_ATTR_RW(brightness);
>
> @@ -215,6 +229,7 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
> #ifdef CONFIG_LEDS_TRIGGERS
> init_rwsem(&led_cdev->trigger_lock);
> #endif
> + mutex_init(&led_cdev->led_lock);
> /* add to the list of leds */
> down_write(&leds_list_lock);
> list_add_tail(&led_cdev->node, &leds_list);
> @@ -266,6 +281,8 @@ void led_classdev_unregister(struct led_classdev *led_cdev)
> down_write(&leds_list_lock);
> list_del(&led_cdev->node);
> up_write(&leds_list_lock);
> +
> + mutex_destroy(&led_cdev->led_lock);
> }
> EXPORT_SYMBOL_GPL(led_classdev_unregister);
>
> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
> index 466ce5a..4649ea5 100644
> --- a/drivers/leds/led-core.c
> +++ b/drivers/leds/led-core.c
> @@ -143,3 +143,21 @@ int led_update_brightness(struct led_classdev *led_cdev)
> return ret;
> }
> EXPORT_SYMBOL(led_update_brightness);
> +
> +/* Caller must ensure led_cdev->led_lock held */
> +void led_sysfs_lock(struct led_classdev *led_cdev)
> +{
> + lockdep_assert_held(&led_cdev->led_lock);
> +
> + led_cdev->flags |= LED_SYSFS_LOCK;
> +}
> +EXPORT_SYMBOL_GPL(led_sysfs_lock);
> +
> +/* Caller must ensure led_cdev->led_lock held */
> +void led_sysfs_unlock(struct led_classdev *led_cdev)
> +{
> + lockdep_assert_held(&led_cdev->led_lock);
> +
> + led_cdev->flags &= ~LED_SYSFS_LOCK;
> +}
> +EXPORT_SYMBOL_GPL(led_sysfs_unlock);
> diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
> index c3734f1..d391a5d 100644
> --- a/drivers/leds/led-triggers.c
> +++ b/drivers/leds/led-triggers.c
> @@ -37,6 +37,11 @@ ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
> char trigger_name[TRIG_NAME_MAX];
> struct led_trigger *trig;
> size_t len;
> + int ret = count;
> +
> +#ifdef CONFIG_V4L2_FLASH_LED_CLASS
> + mutex_lock(&led_cdev->led_lock);
> +#endif
>
> trigger_name[sizeof(trigger_name) - 1] = '\0';
> strncpy(trigger_name, buf, sizeof(trigger_name) - 1);
> @@ -47,7 +52,7 @@ ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
>
> if (!strcmp(trigger_name, "none")) {
> led_trigger_remove(led_cdev);
> - return count;
> + goto exit_unlock;
> }
>
> down_read(&triggers_list_lock);
> @@ -58,12 +63,16 @@ ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
> up_write(&led_cdev->trigger_lock);
>
> up_read(&triggers_list_lock);
> - return count;
> + goto exit_unlock;
> }
> }
> up_read(&triggers_list_lock);
>
> - return -EINVAL;
> +exit_unlock:
> +#ifdef CONFIG_V4L2_FLASH_LED_CLASS
> + mutex_unlock(&led_cdev->led_lock);
> +#endif
> + return ret;
> }
> EXPORT_SYMBOL_GPL(led_trigger_store);
>
> diff --git a/include/linux/leds.h b/include/linux/leds.h
> index cc85b16..ef343f1 100644
> --- a/include/linux/leds.h
> +++ b/include/linux/leds.h
> @@ -13,6 +13,7 @@
> #define __LINUX_LEDS_H_INCLUDED
>
> #include <linux/list.h>
> +#include <linux/mutex.h>
> #include <linux/rwsem.h>
> #include <linux/spinlock.h>
> #include <linux/workqueue.h>
> @@ -41,6 +42,7 @@ struct led_classdev {
> #define LED_BLINK_ONESHOT (1 << 17)
> #define LED_BLINK_ONESHOT_STOP (1 << 18)
> #define LED_BLINK_INVERT (1 << 19)
> +#define LED_SYSFS_LOCK (1 << 20)
>
> /* Set LED brightness level */
> /* Must not sleep, use a workqueue if needed */
> @@ -84,6 +86,9 @@ struct led_classdev {
> /* true if activated - deactivate routine uses it to do cleanup */
> bool activated;
> #endif
> +
> + /* Ensures consistent access to the LED Flash Class device */
> + struct mutex led_lock;
> };
>
> extern int led_classdev_register(struct device *parent,
> @@ -150,6 +155,33 @@ extern void led_set_brightness(struct led_classdev *led_cdev,
> */
> extern int led_update_brightness(struct led_classdev *led_cdev);
>
> +/**
> + * led_sysfs_lock - lock LED sysfs interface
> + * @led_cdev: the LED to set
> + *
> + * Lock the LED's sysfs interface
> + */
> +extern void led_sysfs_lock(struct led_classdev *led_cdev);
> +
> +/**
> + * led_sysfs_unlock - unlock LED sysfs interface
> + * @led_cdev: the LED to set
> + *
> + * Unlock the LED's sysfs interface
> + */
> +extern void led_sysfs_unlock(struct led_classdev *led_cdev);
> +
> +/**
> + * led_sysfs_is_locked
> + * @led_cdev: the LED to query
> + *
> + * Returns: true if the sysfs interface of the led is locked
> + */
> +static inline bool led_sysfs_is_locked(struct led_classdev *led_cdev)
> +{
> + return led_cdev->flags & LED_SYSFS_LOCK;
> +}
> +
> /*
> * LED Triggers
> */
> --
> 1.7.9.5
>
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