[PATCH 2/2] watchdog/uapi: Add WDIOS_{RUN,STOP}_ON_REBOOT

[Dmitry Safonov <dima@arista.com>]

Many watchdog drivers use watchdog_stop_on_reboot() helper in order
to stop the watchdog on system reboot. Unfortunately, this logic is
coded in driver's probe function and doesn't allows user to decide what
to do during shutdown/reboot.

On the other side, Xen and Qemu watchdog drivers (xen_wdt and i6300esb)
may be configured to either send NMI or turn off/reboot VM as
the watchdog action. As the kernel may stuck at any state, sending NMIs
can't reliably reboot the VM.

At Arista, we benefited from the following set-up: the emulated watchdogs
trigger VM reset and softdog is set to catch less severe conditions to
generate vmcore. Just before reboot watchdog's timeout is increased
to some good-enough value (3 mins). That keeps watchdog always running
and guarantees that VM doesn't stuck.

Provide new WDIOS_RUN_ON_REBOOT and WDIOS_STOP_ON_REBOOT ioctl options
to set up strategy on reboot.

Signed-off-by: Dmitry Safonov <dima@arista.com>
---
 drivers/watchdog/watchdog_dev.c | 12 ++++++++++++
 include/linux/watchdog.h        |  6 ++++++
 include/uapi/linux/watchdog.h   |  3 ++-
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 8b5c742f24e8..c854cd0245db 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -753,6 +753,18 @@ static long watchdog_ioctl(struct file *file, unsigned int cmd,
 		}
 		if (val & WDIOS_ENABLECARD)
 			err = watchdog_start(wdd);
+
+		if (val & WDIOS_RUN_ON_REBOOT) {
+			if (val & WDIOS_STOP_ON_REBOOT) {
+				err = -EINVAL;
+				break;
+			}
+			watchdog_run_on_reboot(wdd);
+			err = 0;
+		} else if (val & WDIOS_STOP_ON_REBOOT) {
+			watchdog_stop_on_reboot(wdd);
+			err = 0;
+		}
 		break;
 	case WDIOC_KEEPALIVE:
 		if (!(wdd->info->options & WDIOF_KEEPALIVEPING)) {
diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
index 417d9f37077a..9e2ca7754631 100644
--- a/include/linux/watchdog.h
+++ b/include/linux/watchdog.h
@@ -150,6 +150,12 @@ static inline void watchdog_stop_on_reboot(struct watchdog_device *wdd)
 	set_bit(WDOG_STOP_ON_REBOOT, &wdd->status);
 }
 
+/* Use the following function to keep the watchdog running on reboot */
+static inline void watchdog_run_on_reboot(struct watchdog_device *wdd)
+{
+	clear_bit(WDOG_STOP_ON_REBOOT, &wdd->status);
+}
+
 /* Use the following function to stop the watchdog when unregistering it */
 static inline void watchdog_stop_on_unregister(struct watchdog_device *wdd)
 {
diff --git a/include/uapi/linux/watchdog.h b/include/uapi/linux/watchdog.h
index b15cde5c9054..bf19a5d3c987 100644
--- a/include/uapi/linux/watchdog.h
+++ b/include/uapi/linux/watchdog.h
@@ -53,6 +53,7 @@ struct watchdog_info {
 #define	WDIOS_DISABLECARD	0x0001	/* Turn off the watchdog timer */
 #define	WDIOS_ENABLECARD	0x0002	/* Turn on the watchdog timer */
 #define	WDIOS_TEMPPANIC		0x0004	/* Kernel panic on temperature trip */
-
+#define	WDIOS_RUN_ON_REBOOT	0x0008	/* Keep watchdog enabled on reboot */
+#define	WDIOS_STOP_ON_REBOOT	0x0010	/* Turn off the watchdog on reboot */
 
 #endif /* _UAPI_LINUX_WATCHDOG_H */
-- 
2.25.0