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Message-ID: <20130412151826.GC28704@roeck-us.net>
Date: Fri, 12 Apr 2013 08:18:26 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: "Kim, Milo" <Milo.Kim@...com>
Cc: "wim@...ana.be" <wim@...ana.be>,
"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] watchdog: introduce new watchdog AUTOSTART option
On Fri, Apr 12, 2013 at 06:51:47AM +0000, Kim, Milo wrote:
> Conventionally, watchdog timer driver is activated by an user space request.
> This patch enables an automatic start/ping operation of a watchdog without an
> application.
>
> (a) Work flow
> If a watchdog timer driver is configured with WDIOF_AUTOSTART option,
> then it starts and ping automatically on watchdog device registration.
> A delayed workqueue invokes a ping operation of the watchdog periodically.
> In the mean time, if an application tries to open the watchdog device,
> it returns as -EBUSY because the watchdog is already running.
> When the watchdog is unregistered, timed workqueue is canceled.
>
> (b) Structure changes
> ping_period : Period time for watchdog ping. Unit is millisecond.
> work : Workqueue for automatic ping operation.
> WDOG_AUTOSTARTED : Added status bit. Set when ping is done.
> Cleared when period time is expired.
> WDIOF_AUTOSTART : New option flag.
>
> (c) Documentation
> It describes how it works and how to use this feature in a watchdog driver.
>
> Signed-off-by: Milo(Woogyom) Kim <milo.kim@...com>
I really don't like that idea. It defeats a significant part of the purpose
for having a watchdog, which is to prevent user-space hangups.
To make this a driver option is even more odd - it forces every user of this
driver to use it in-kernel only, and makes /dev/watchdog quite useless.
I mean, really, if you have such a watchdog, what is the point of using the
watchdog infrastructure in the first place ? Just make it a kernel thread or
timer-activated platform code which pings your watchdog once in a while. No
need to get the watchdog infrastructure involved in the first place.
Am I missing something ?
Thanks,
Guenter
> ---
> Documentation/watchdog/watchdog-without-app.txt | 59 ++++++++++++++++
> drivers/watchdog/watchdog_dev.c | 86 ++++++++++++++++++++++-
> include/linux/watchdog.h | 6 ++
> include/uapi/linux/watchdog.h | 1 +
> 4 files changed, 151 insertions(+), 1 deletion(-)
> create mode 100644 Documentation/watchdog/watchdog-without-app.txt
>
> diff --git a/Documentation/watchdog/watchdog-without-app.txt b/Documentation/watchdog/watchdog-without-app.txt
> new file mode 100644
> index 0000000..596a30a
> --- /dev/null
> +++ b/Documentation/watchdog/watchdog-without-app.txt
> @@ -0,0 +1,59 @@
> +The Linux WatchDog Timer Driver without an Application
> +======================================================
> +
> +Milo Kim <milo.kim@...com>
> +
> +Introduction
> +------------
> +Linux WatchDog Timer (WDT) driver is activated by an user space request.
> +If a WDT needs to be enabled alone, without an application, you can configure
> +the WDT driver with 'AUTOSTART' option.
> +
> +How it works
> +------------
> +* Conventional watchdog system
> +
> + (WDT driver) ------------ (WDT Application)
> + register --> WDT Core
> + ------------
> + .start <-- WDT Dev /dev/watchdogN <-- open
> + .ping ------------ . ioctl - keepalive
> + .stop . close
> + .
> + activated by an application
> +
> +* Watchdog autostart feature
> +
> + (WDT driver) ------------
> + register --> WDT Core
> + ------------
> + .start <-- WDT Dev /dev/watchdogN
> + .ping . ------------
> + .
> + .
> + start and ping periodically without an application
> +
> +How to use
> +----------
> +1) Add 'WDIOF_AUTOSTART' option in your watchdog_info.
> +
> +static const struct watchdog_info foo_wdt_info = {
> + .options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_AUTOSTART,
> + .identity = "Auto Watchdog Sample",
> +};
> +
> +2) Define the value of 'ping_period' in your watchdog_device structure.
> + Unit is millisecond.
> +
> +static int foo_wdt_probe(struct platform_device *pdev)
> +{
> + struct watchdog_device *foo_wdt;
> +
> + foo_wdt->info = &foo_wdt_info;
> + foo_wdt->ops = &foo_wdt_ops;
> + foo_wdt->ping_period = 1000; /* kick a watchdog per 1 sec */
> +
> + return watchdog_register_device(foo_wdt);
> +}
> +
> +Then the foo watchdog is started and ping periodically without an application.
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 08b48bb..42bfc9a 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -44,6 +44,8 @@
>
> #include "watchdog_core.h"
>
> +#define MAX_PING_PERIOD (60 * 60 * 1000) /* 1 hour */
> +
> /* the dev_t structure to store the dynamically allocated watchdog devices */
> static dev_t watchdog_devt;
> /* the watchdog device behind /dev/watchdog */
> @@ -115,6 +117,70 @@ out_start:
> return err;
> }
>
> +static void watchdog_set_autostart(struct watchdog_device *wdd)
> +{
> + schedule_delayed_work(&wdd->work, msecs_to_jiffies(wdd->ping_period));
> + set_bit(WDOG_AUTOSTARTED, &wdd->status);
> +}
> +
> +static void watchdog_clear_autostart(struct watchdog_device *wdd)
> +{
> + clear_bit(WDOG_AUTOSTARTED, &wdd->status);
> +}
> +
> +static bool watchdog_autostarted(struct watchdog_device *wdd)
> +{
> + return test_bit(WDOG_AUTOSTARTED, &wdd->status);
> +}
> +
> +static void watchdog_autoping_work(struct work_struct *w)
> +{
> + struct watchdog_device *wdd = container_of(w, struct watchdog_device,
> + work.work);
> + int err;
> +
> + if (!watchdog_autostarted(wdd))
> + return;
> +
> + watchdog_clear_autostart(wdd);
> +
> + err = watchdog_ping(wdd);
> + if (err)
> + return;
> +
> + watchdog_set_autostart(wdd);
> +}
> +
> +/*
> + * watchdog_auto_start: start the watchdong and ping it
> + * @wdd: the watchdog device to start
> + *
> + * If watchdog_info has WDIOF_AUTOSTART option, then the watchdog
> + * starts automatically. Ping operation is done by internal timer.
> + * The watchdog driver is activated without a watchdog user application.
> + * This function should be used by the watchdog driver, not an user-space
> + * interface.
> + */
> +
> +static int watchdog_auto_start(struct watchdog_device *wdd)
> +{
> + int err;
> +
> + if (wdd->ping_period < 1 || wdd->ping_period >= MAX_PING_PERIOD) {
> + pr_err("invalid ping time value:%u\n", wdd->ping_period);
> + return -EINVAL;
> + }
> +
> + err = watchdog_start(wdd);
> + if (err)
> + return err;
> +
> + INIT_DELAYED_WORK(&wdd->work, watchdog_autoping_work);
> + watchdog_set_autostart(wdd);
> +
> + return 0;
> +}
> +
> /*
> * watchdog_stop: wrapper to stop the watchdog.
> * @wddev: the watchdog device to stop
> @@ -420,7 +486,8 @@ static int watchdog_open(struct inode *inode, struct file *file)
> wdd = container_of(inode->i_cdev, struct watchdog_device, cdev);
>
> /* the watchdog is single open! */
> - if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status))
> + if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status) ||
> + watchdog_autostarted(wdd))
> return -EBUSY;
>
> /*
> @@ -550,7 +617,21 @@ int watchdog_dev_register(struct watchdog_device *watchdog)
> misc_deregister(&watchdog_miscdev);
> old_wdd = NULL;
> }
> + return err;
> + }
> +
> + /* Activate the watchdog automatically by the driver itself */
> + if (watchdog->info->options & WDIOF_AUTOSTART) {
> + err = watchdog_auto_start(watchdog);
> + if (err) {
> + cdev_del(&watchdog->cdev);
> + if (watchdog->id == 0) {
> + misc_deregister(&watchdog_miscdev);
> + old_wdd = NULL;
> + }
> + }
> }
> +
> return err;
> }
>
> @@ -563,6 +644,9 @@ int watchdog_dev_register(struct watchdog_device *watchdog)
>
> int watchdog_dev_unregister(struct watchdog_device *watchdog)
> {
> + if (watchdog_autostarted(watchdog))
> + cancel_delayed_work_sync(&watchdog->work);
> +
> mutex_lock(&watchdog->lock);
> set_bit(WDOG_UNREGISTERED, &watchdog->status);
> mutex_unlock(&watchdog->lock);
> diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
> index 2a3038e..4b7478a 100644
> --- a/include/linux/watchdog.h
> +++ b/include/linux/watchdog.h
> @@ -62,6 +62,9 @@ struct watchdog_ops {
> * @timeout: The watchdog devices timeout value.
> * @min_timeout:The watchdog devices minimum timeout value.
> * @max_timeout:The watchdog devices maximum timeout value.
> + * @ping_period:Period time for watchdog ping. Unit is millisecond.
> + * Only valid with WDIOF_AUTOSTART.
> + * @work: Workqueue for handling auto ping
> * @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.
> @@ -86,6 +89,8 @@ struct watchdog_device {
> unsigned int timeout;
> unsigned int min_timeout;
> unsigned int max_timeout;
> + unsigned int ping_period;
> + struct delayed_work work;
> void *driver_data;
> struct mutex lock;
> unsigned long status;
> @@ -95,6 +100,7 @@ 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 */
> +#define WDOG_AUTOSTARTED 5 /* Started and kicked automatically */
> };
>
> #ifdef CONFIG_WATCHDOG_NOWAYOUT
> diff --git a/include/uapi/linux/watchdog.h b/include/uapi/linux/watchdog.h
> index 2babe72..9095ec8 100644
> --- a/include/uapi/linux/watchdog.h
> +++ b/include/uapi/linux/watchdog.h
> @@ -47,6 +47,7 @@ struct watchdog_info {
> #define WDIOF_PRETIMEOUT 0x0200 /* Pretimeout (in seconds), get/set */
> #define WDIOF_ALARMONLY 0x0400 /* Watchdog triggers a management or
> other external alarm not a reboot */
> +#define WDIOF_AUTOSTART 0x1000 /* Start and ping automatically */
> #define WDIOF_KEEPALIVEPING 0x8000 /* Keep alive ping reply */
>
> #define WDIOS_DISABLECARD 0x0001 /* Turn off the watchdog timer */
> --
> 1.7.9.5
>
>
> Best Regards,
> Milo
>
>
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