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SubjectRe: [PATCH v3 1/2] watchdog_core: Add watchdog registration deferral mechanism
On 06/06/2015 12:46 AM, Jean-Baptiste Theou wrote:
> Currently, watchdog subsystem require the misc subsystem to
> register a watchdog. This may not be the case in case of an
> early registration of a watchdog, which can be required when
> the watchdog cannot be disabled.
>
> This patch introduces a deferral mechanism to remove this requirement.
>
Couple of comments, but almost good.

Thanks,
Guenter

> Signed-off-by: Jean-Baptiste Theou <jtheou@adeneo-embedded.us>
> ---
> Changes in v3:
> - Adjust patch based on Guenter feedbacks
> - Fix watchdog_deferred_registration_del
> - Fix typos
>
> Documentation/watchdog/watchdog-kernel-api.txt | 7 ++
> drivers/watchdog/watchdog_core.c | 114 +++++++++++++++++++++----
> include/linux/watchdog.h | 3 +
> 3 files changed, 106 insertions(+), 18 deletions(-)
>
> diff --git a/Documentation/watchdog/watchdog-kernel-api.txt b/Documentation/watchdog/watchdog-kernel-api.txt
> index a0438f3..e83518c 100644
> --- a/Documentation/watchdog/watchdog-kernel-api.txt
> +++ b/Documentation/watchdog/watchdog-kernel-api.txt
> @@ -36,6 +36,10 @@ The watchdog_unregister_device routine deregisters a registered watchdog timer
> device. The parameter of this routine is the pointer to the registered
> watchdog_device structure.
>
> +The watchdog subsystem includes an registration deferral mechanism,
> +which allows you to register an watchdog as early as you wish during
> +the boot process.
> +
> The watchdog device structure looks like this:
>
> struct watchdog_device {
> @@ -52,6 +56,7 @@ struct watchdog_device {
> void *driver_data;
> struct mutex lock;
> unsigned long status;
> + struct list_head deferred_registration;
> };
>
> It contains following fields:
> @@ -80,6 +85,8 @@ It contains following fields:
> information about the status of the device (Like: is the watchdog timer
> running/active, is the nowayout bit set, is the device opened via
> the /dev/watchdog interface or not, ...).
> +* deferred_registration: entry in deferred_registration_list which is used to
> + register early initialized watchdogs.
>
> The list of watchdog operations is defined as:
>
> diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
> index cec9b55..7dba8d9 100644
> --- a/drivers/watchdog/watchdog_core.c
> +++ b/drivers/watchdog/watchdog_core.c
> @@ -43,6 +43,43 @@
> static DEFINE_IDA(watchdog_ida);
> static struct class *watchdog_class;
>
> +/*
> + * Deferred Registration infrastructure.
> + *
> + * Sometimes watchdog drivers needs to be loaded as soon as possible,
> + * for example when it's impossible to disable it. To do so,
> + * raising the initcall level of the watchdog driver is a solution.
> + * But in such case, the miscdev is maybe not ready (subsys_initcall), and
> + * watchdog_core need miscdev to register the watchdog as a char device.
> + *
> + * The deferred registration infrastructure offer a way for the watchdog
> + * subsystem to register a watchdog properly, even before miscdev is ready.
> + */
> +
> +static DEFINE_MUTEX(watchdog_deferred_registration_mutex);
> +static LIST_HEAD(watchdog_deferred_registration_pending_list);
> +static bool watchdog_deferred_registration_done;
> +
> +static int watchdog_deferred_registration_add(struct watchdog_device *wdd)
> +{
> + list_add_tail(&wdd->deferred_registration,
> + &watchdog_deferred_registration_pending_list);

Please align the continuation line with '('.

> + return 0;
> +}
> +
> +static void watchdog_deferred_registration_del(struct watchdog_device *wdd)
> +{
> + struct list_head *p, *n;
> + struct watchdog_device *wdd_tmp;
> +
> + list_for_each_safe(p, n, &watchdog_deferred_registration_pending_list) {
> + wdd_tmp = list_entry(p, struct watchdog_device,
> + deferred_registration);
> + if (wdd_tmp == wdd)
> + list_del(&wdd_tmp->deferred_registration);

You can break out of the loop here. No need to check the rest of the entries.

> + }
> +}
> +
> static void watchdog_check_min_max_timeout(struct watchdog_device *wdd)
> {
> /*
> @@ -98,17 +135,7 @@ int watchdog_init_timeout(struct watchdog_device *wdd,
> }
> EXPORT_SYMBOL_GPL(watchdog_init_timeout);
>
> -/**
> - * watchdog_register_device() - register a watchdog device
> - * @wdd: watchdog device
> - *
> - * Register a watchdog device with the kernel so that the
> - * watchdog timer can be accessed from userspace.
> - *
> - * A zero is returned on success and a negative errno code for
> - * failure.
> - */
> -int watchdog_register_device(struct watchdog_device *wdd)
> +static int __watchdog_register_device(struct watchdog_device *wdd)
> {
> int ret, id, devno;
>
> @@ -164,16 +191,33 @@ int watchdog_register_device(struct watchdog_device *wdd)
>
> return 0;
> }
> -EXPORT_SYMBOL_GPL(watchdog_register_device);
>
> /**
> - * watchdog_unregister_device() - unregister a watchdog device
> - * @wdd: watchdog device to unregister
> + * watchdog_register_device() - register a watchdog device
> + * @wdd: watchdog device
> *
> - * Unregister a watchdog device that was previously successfully
> - * registered with watchdog_register_device().
> + * Register a watchdog device with the kernel so that the
> + * watchdog timer can be accessed from userspace.
> + *
> + * A zero is returned on success and a negative errno code for
> + * failure.
> */
> -void watchdog_unregister_device(struct watchdog_device *wdd)
> +
> +int watchdog_register_device(struct watchdog_device *wdd)
> +{
> + int ret;
> +
> + mutex_lock(&watchdog_deferred_registration_mutex);
> + if (watchdog_deferred_registration_done)
> + ret = __watchdog_register_device(wdd);
> + else
> + ret = watchdog_deferred_registration_add(wdd);
> + mutex_unlock(&watchdog_deferred_registration_mutex);
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(watchdog_register_device);
> +
> +static void __watchdog_unregister_device(struct watchdog_device *wdd)
> {
> int ret;
> int devno;
> @@ -189,8 +233,41 @@ void watchdog_unregister_device(struct watchdog_device *wdd)
> ida_simple_remove(&watchdog_ida, wdd->id);
> wdd->dev = NULL;
> }
> +
> +/**
> + * watchdog_unregister_device() - unregister a watchdog device
> + * @wdd: watchdog device to unregister
> + *
> + * Unregister a watchdog device that was previously successfully
> + * registered with watchdog_register_device().
> + */
> +
> +void watchdog_unregister_device(struct watchdog_device *wdd)
> +{
> + mutex_lock(&watchdog_deferred_registration_mutex);
> + if (watchdog_deferred_registration_done)
> + __watchdog_unregister_device(wdd);
> + else
> + watchdog_deferred_registration_del(wdd);
> + mutex_unlock(&watchdog_deferred_registration_mutex);
> +}
> +
> EXPORT_SYMBOL_GPL(watchdog_unregister_device);
>
> +static int __init watchdog_deferred_registration(void)
> +{
> + mutex_lock(&watchdog_deferred_registration_mutex);
> + watchdog_deferred_registration_done = true;
> + while (!list_empty(&watchdog_deferred_registration_pending_list)) {
> + struct watchdog_device *wdd = list_first_entry(&watchdog_deferred_registration_pending_list,
> + struct watchdog_device, deferred_registration);

Please watch out for line length.

struct watchdog_device *wdd;

wdd = list_first_entry(&watchdog_deferred_registration_pending_list,
struct watchdog_device, deferred_registration);

might work better here.

> + list_del(&wdd->deferred_registration);
> + __watchdog_register_device(wdd);
> + }
> + mutex_unlock(&watchdog_deferred_registration_mutex);
> + return 0;
> +}
> +
> static int __init watchdog_init(void)
> {
> int err;
> @@ -207,6 +284,7 @@ static int __init watchdog_init(void)
> return err;
> }
>
> + watchdog_deferred_registration();
> return 0;
> }
>
> @@ -217,7 +295,7 @@ static void __exit watchdog_exit(void)
> ida_destroy(&watchdog_ida);
> }
>
> -subsys_initcall(watchdog_init);
> +subsys_initcall_sync(watchdog_init);
> module_exit(watchdog_exit);
>
> MODULE_AUTHOR("Alan Cox <alan@lxorguk.ukuu.org.uk>");
> diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
> index a746bf5..f9bb943 100644
> --- a/include/linux/watchdog.h
> +++ b/include/linux/watchdog.h
> @@ -65,6 +65,8 @@ struct watchdog_ops {
> * @driver-data:Pointer to the drivers private data.
> * @lock: Lock for watchdog core internal use only.
> * @status: Field that contains the devices internal status bits.
> + * @deferred_registration: entry in deferred_registration_list which is used to
> + * register early initialized watchdogs.
> *
> * The watchdog_device structure contains all information about a
> * watchdog timer device.
> @@ -95,6 +97,7 @@ struct watchdog_device {
> #define WDOG_ALLOW_RELEASE 2 /* Did we receive the magic char ? */
> #define WDOG_NO_WAY_OUT 3 /* Is 'nowayout' feature set ? */
> #define WDOG_UNREGISTERED 4 /* Has the device been unregistered */
> + struct list_head deferred_registration;
> };
>
> #define WATCHDOG_NOWAYOUT IS_BUILTIN(CONFIG_WATCHDOG_NOWAYOUT)
>



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