Re: [PATCH 1/5] watchdog: Create watchdog device in watchdog_dev.c

[Damien Riegel <damien.riegel@savoirfairelinux.com>]

On Sun, Dec 20, 2015 at 01:04:59PM -0800, Guenter Roeck wrote:
> The watchdog character device is currently created in watchdog_dev.c,
> and the watchdog device in watchdog_core.c. This results in
> cross-dependencies, since device creation needs to know the watchdog
> character device number as well as the watchdog class, both of which
> reside in watchdog_dev.c.
> 
> Create the watchdog device in watchdog_dev.c to simplify the code.
> 
> Inspired by earlier patch set from Damien Riegel.

Hi Guenter,

The main purpose of my patch was to inverse the device creation and the
cdev registration to avoid a racy situation, bu you have dropped that in
this version. Is there a reason for that?

Thanks,
Damien

> 
> Cc: Damien Riegel <damien.riegel@savoirfairelinux.com>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
>  drivers/watchdog/watchdog_core.c | 33 ++++--------------
>  drivers/watchdog/watchdog_core.h |  4 +--
>  drivers/watchdog/watchdog_dev.c  | 73 +++++++++++++++++++++++++++++++++-------
>  3 files changed, 69 insertions(+), 41 deletions(-)
> 
> diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
> index 551af042867c..f0293f7d2b80 100644
> --- a/drivers/watchdog/watchdog_core.c
> +++ b/drivers/watchdog/watchdog_core.c
> @@ -42,7 +42,6 @@
>  #include "watchdog_core.h"	/* For watchdog_dev_register/... */
>  
>  static DEFINE_IDA(watchdog_ida);
> -static struct class *watchdog_class;
>  
>  /*
>   * Deferred Registration infrastructure.
> @@ -194,7 +193,7 @@ EXPORT_SYMBOL_GPL(watchdog_set_restart_priority);
>  
>  static int __watchdog_register_device(struct watchdog_device *wdd)
>  {
> -	int ret, id = -1, devno;
> +	int ret, id = -1;
>  
>  	if (wdd == NULL || wdd->info == NULL || wdd->ops == NULL)
>  		return -EINVAL;
> @@ -247,16 +246,6 @@ static int __watchdog_register_device(struct watchdog_device *wdd)
>  		}
>  	}
>  
> -	devno = wdd->cdev.dev;
> -	wdd->dev = device_create(watchdog_class, wdd->parent, devno,
> -					wdd, "watchdog%d", wdd->id);
> -	if (IS_ERR(wdd->dev)) {
> -		watchdog_dev_unregister(wdd);
> -		ida_simple_remove(&watchdog_ida, id);
> -		ret = PTR_ERR(wdd->dev);
> -		return ret;
> -	}
> -
>  	if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status)) {
>  		wdd->reboot_nb.notifier_call = watchdog_reboot_notifier;
>  
> @@ -265,9 +254,7 @@ static int __watchdog_register_device(struct watchdog_device *wdd)
>  			dev_err(wdd->dev, "Cannot register reboot notifier (%d)\n",
>  				ret);
>  			watchdog_dev_unregister(wdd);
> -			device_destroy(watchdog_class, devno);
>  			ida_simple_remove(&watchdog_ida, wdd->id);
> -			wdd->dev = NULL;
>  			return ret;
>  		}
>  	}
> @@ -311,9 +298,6 @@ EXPORT_SYMBOL_GPL(watchdog_register_device);
>  
>  static void __watchdog_unregister_device(struct watchdog_device *wdd)
>  {
> -	int ret;
> -	int devno;
> -
>  	if (wdd == NULL)
>  		return;
>  
> @@ -323,13 +307,8 @@ static void __watchdog_unregister_device(struct watchdog_device *wdd)
>  	if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status))
>  		unregister_reboot_notifier(&wdd->reboot_nb);
>  
> -	devno = wdd->cdev.dev;
> -	ret = watchdog_dev_unregister(wdd);
> -	if (ret)
> -		pr_err("error unregistering /dev/watchdog (err=%d)\n", ret);
> -	device_destroy(watchdog_class, devno);
> +	watchdog_dev_unregister(wdd);
>  	ida_simple_remove(&watchdog_ida, wdd->id);
> -	wdd->dev = NULL;
>  }
>  
>  /**
> @@ -370,9 +349,11 @@ static int __init watchdog_deferred_registration(void)
>  
>  static int __init watchdog_init(void)
>  {
> -	watchdog_class = watchdog_dev_init();
> -	if (IS_ERR(watchdog_class))
> -		return PTR_ERR(watchdog_class);
> +	int err;
> +
> +	err = watchdog_dev_init();
> +	if (err < 0)
> +		return err;
>  
>  	watchdog_deferred_registration();
>  	return 0;
> diff --git a/drivers/watchdog/watchdog_core.h b/drivers/watchdog/watchdog_core.h
> index 1c8d6b0e68c7..86ff962d1e15 100644
> --- a/drivers/watchdog/watchdog_core.h
> +++ b/drivers/watchdog/watchdog_core.h
> @@ -32,6 +32,6 @@
>   *	Functions/procedures to be called by the core
>   */
>  extern int watchdog_dev_register(struct watchdog_device *);
> -extern int watchdog_dev_unregister(struct watchdog_device *);
> -extern struct class * __init watchdog_dev_init(void);
> +extern void watchdog_dev_unregister(struct watchdog_device *);
> +extern int __init watchdog_dev_init(void);
>  extern void __exit watchdog_dev_exit(void);
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index d93118e97d11..c24392623e98 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -626,17 +626,18 @@ static struct miscdevice watchdog_miscdev = {
>  };
>  
>  /*
> - *	watchdog_dev_register: register a watchdog device
> + *	watchdog_cdev_register: register watchdog character device
>   *	@wdd: watchdog device
> + *	@devno: character device number
>   *
> - *	Register a watchdog device including handling the legacy
> + *	Register a watchdog character device including handling the legacy
>   *	/dev/watchdog node. /dev/watchdog is actually a miscdevice and
>   *	thus we set it up like that.
>   */
>  
> -int watchdog_dev_register(struct watchdog_device *wdd)
> +static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
>  {
> -	int err, devno;
> +	int err;
>  
>  	if (wdd->id == 0) {
>  		old_wdd = wdd;
> @@ -654,7 +655,6 @@ int watchdog_dev_register(struct watchdog_device *wdd)
>  	}
>  
>  	/* Fill in the data structures */
> -	devno = MKDEV(MAJOR(watchdog_devt), wdd->id);
>  	cdev_init(&wdd->cdev, &watchdog_fops);
>  	wdd->cdev.owner = wdd->ops->owner;
>  
> @@ -672,13 +672,14 @@ int watchdog_dev_register(struct watchdog_device *wdd)
>  }
>  
>  /*
> - *	watchdog_dev_unregister: unregister a watchdog device
> + *	watchdog_cdev_unregister: unregister watchdog character device
>   *	@watchdog: watchdog device
>   *
> - *	Unregister the watchdog and if needed the legacy /dev/watchdog device.
> + *	Unregister watchdog character device and if needed the legacy
> + *	/dev/watchdog device.
>   */
>  
> -int watchdog_dev_unregister(struct watchdog_device *wdd)
> +static void watchdog_cdev_unregister(struct watchdog_device *wdd)
>  {
>  	mutex_lock(&wdd->lock);
>  	set_bit(WDOG_UNREGISTERED, &wdd->status);
> @@ -689,7 +690,6 @@ int watchdog_dev_unregister(struct watchdog_device *wdd)
>  		misc_deregister(&watchdog_miscdev);
>  		old_wdd = NULL;
>  	}
> -	return 0;
>  }
>  
>  static struct class watchdog_class = {
> @@ -701,29 +701,76 @@ static struct class watchdog_class = {
>  };
>  
>  /*
> + *	watchdog_dev_register: register a watchdog device
> + *	@wdd: watchdog device
> + *
> + *	Register a watchdog device including handling the legacy
> + *	/dev/watchdog node. /dev/watchdog is actually a miscdevice and
> + *	thus we set it up like that.
> + */
> +
> +int watchdog_dev_register(struct watchdog_device *wdd)
> +{
> +	struct device *dev;
> +	dev_t devno;
> +	int ret;
> +
> +	devno = MKDEV(MAJOR(watchdog_devt), wdd->id);
> +
> +	ret = watchdog_cdev_register(wdd, devno);
> +	if (ret)
> +		return ret;
> +
> +	dev = device_create(&watchdog_class, wdd->parent, devno, wdd,
> +			    "watchdog%d", wdd->id);
> +	if (IS_ERR(dev)) {
> +		watchdog_cdev_unregister(wdd);
> +		return PTR_ERR(dev);
> +	}
> +	wdd->dev = dev;
> +
> +	return ret;
> +}
> +
> +/*
> + *	watchdog_dev_unregister: unregister a watchdog device
> + *	@watchdog: watchdog device
> + *
> + *	Unregister watchdog device and if needed the legacy
> + *	/dev/watchdog device.
> + */
> +
> +void watchdog_dev_unregister(struct watchdog_device *wdd)
> +{
> +	watchdog_cdev_unregister(wdd);
> +	device_destroy(&watchdog_class, wdd->dev->devt);
> +	wdd->dev = NULL;
> +}
> +
> +/*
>   *	watchdog_dev_init: init dev part of watchdog core
>   *
>   *	Allocate a range of chardev nodes to use for watchdog devices
>   */
>  
> -struct class * __init watchdog_dev_init(void)
> +int __init watchdog_dev_init(void)
>  {
>  	int err;
>  
>  	err = class_register(&watchdog_class);
>  	if (err < 0) {
>  		pr_err("couldn't register class\n");
> -		return ERR_PTR(err);
> +		return err;
>  	}
>  
>  	err = alloc_chrdev_region(&watchdog_devt, 0, MAX_DOGS, "watchdog");
>  	if (err < 0) {
>  		pr_err("watchdog: unable to allocate char dev region\n");
>  		class_unregister(&watchdog_class);
> -		return ERR_PTR(err);
> +		return err;
>  	}
>  
> -	return &watchdog_class;
> +	return 0;
>  }
>  
>  /*
> -- 
> 2.1.4
>