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SubjectRe: [RFC][PATCH] watchdog: rti-wdt: Provide set_timeout handler to make existing userspace happy
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On 9/13/21 4:41 AM, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@siemens.com>
>
> Prominent userspace - systemd - cannot handle watchdogs without
> WDIOF_SETTIMEOUT, even if it was configured to the same time as the
> driver selected or was used by firmware to start the watchdog. To avoid
> failing in this case, implement a handler that only fails if a deviating
> set_timeout is requested.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

NACK. This is a userspace problem. The ABI clearly states that
WDIOF_SETTIMEOUT is optional, and userspace must not depend on it.
We can not start making kernel changes just to make broken userspace
code happy. systemd should be fixed instead.

Guenter

> ---
>
> See also https://github.com/systemd/systemd/issues/20683
>
> drivers/watchdog/rti_wdt.c | 17 ++++++++++++++++-
> 1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
> index 359302f71f7e..365255b15a0d 100644
> --- a/drivers/watchdog/rti_wdt.c
> +++ b/drivers/watchdog/rti_wdt.c
> @@ -173,13 +173,27 @@ static unsigned int rti_wdt_get_timeleft_ms(struct watchdog_device *wdd)
> return timer_counter;
> }
>
> +static int rti_wdt_set_timeout(struct watchdog_device *wdd,
> + unsigned int timeout)
> +{
> + /*
> + * Updating the timeout after start is actually not supported, but
> + * let's ignore requests for the already configured value. Helps
> + * existing userspace such as systemd.
> + */
> + if (timeout != heartbeat)
> + return -EOPNOTSUPP;
> +
> + return 0;
> +}
> +
> static unsigned int rti_wdt_get_timeleft(struct watchdog_device *wdd)
> {
> return rti_wdt_get_timeleft_ms(wdd) / 1000;
> }
>
> static const struct watchdog_info rti_wdt_info = {
> - .options = WDIOF_KEEPALIVEPING,
> + .options = WDIOF_KEEPALIVEPING | WDIOF_SETTIMEOUT,
> .identity = "K3 RTI Watchdog",
> };
>
> @@ -187,6 +201,7 @@ static const struct watchdog_ops rti_wdt_ops = {
> .owner = THIS_MODULE,
> .start = rti_wdt_start,
> .ping = rti_wdt_ping,
> + .set_timeout = rti_wdt_set_timeout,
> .get_timeleft = rti_wdt_get_timeleft,
> };
>
>

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