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    SubjectRe: [PATCH v2] leds: heartbeat: stop on shutdown
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    On Tue, 2012-04-24 at 18:32 +0200, Alexander Holler wrote:
    > Am 24.04.2012 17:24, schrieb Shuah Khan:
    > > On Tue, 2012-04-24 at 17:07 +0200, Alexander Holler wrote:
    > >> A halted kernel should not show a heartbeat.
    > >>
    > >> Signed-off-by: Alexander Holler <holler@ahsoftware.de>
    > >> ---
    > >> drivers/leds/ledtrig-heartbeat.c | 18 +++++++++++++++++-
    > >> 1 files changed, 17 insertions(+), 1 deletions(-)
    > >>
    > >> diff --git a/drivers/leds/ledtrig-heartbeat.c b/drivers/leds/ledtrig-heartbeat.c
    > >> index 759c0bb..1c05bd9 100644
    > >> --- a/drivers/leds/ledtrig-heartbeat.c
    > >> +++ b/drivers/leds/ledtrig-heartbeat.c
    > >> @@ -18,6 +18,7 @@
    > >> #include <linux/timer.h>
    > >> #include <linux/sched.h>
    > >> #include <linux/leds.h>
    > >> +#include <linux/reboot.h>
    > >> #include "leds.h"
    > >>
    > >> struct heartbeat_trig_data {
    > >> @@ -101,13 +102,28 @@ static struct led_trigger heartbeat_led_trigger = {
    > >> .deactivate = heartbeat_trig_deactivate,
    > >> };
    > >>
    > >> +static int heartbeat_reboot_notifier(struct notifier_block *nb,
    > >> + unsigned long code, void *unused)
    > >> +{
    > >> + led_trigger_unregister(&heartbeat_led_trigger);
    > >> + return NOTIFY_DONE;
    > >> +}
    I am sorry I didn't catch this the last time. Do you need to call
    unregister here? Looks like trigger is going away with a registered
    reboot notifier. Might be fine, since reboot is going to happen.

    > >> +
    > >> +static struct notifier_block heartbeat_reboot_nb = {
    > >> + .notifier_call = heartbeat_reboot_notifier,
    > >> +};
    > >> +
    > >> static int __init heartbeat_trig_init(void)
    > >> {
    > >> - return led_trigger_register(&heartbeat_led_trigger);
    > >> + int rc = led_trigger_register(&heartbeat_led_trigger);
    > >> + if( ! rc )
    > >> + register_reboot_notifier(&heartbeat_reboot_nb);
    > >
    > > Do you need to check return value here? I see return value being checked
    > > in some places in the kernel and not in others. Not checking is fine for
    > > now since register_reboot_notifier() always returns 0.
    > >
    > > Maybe adding return handling might not be a bad idea to be consistent
    > > with other places that do check.
    >
    > What to do if it fails? As long as unregister_reboot_notifier() doesn't
    > do something bad with non-registered notifiers (which it doesn't), I
    > would let the init still succeed.

    Yes I agree that init should still succeed. It might be helpful to throw
    out a kernel message when this occurs though since register shouldn't
    fail unless there is an error.

    > And to not unregister a
    > non-registered-reboot_notifier, a long-living bool would be needed.

    Yes keeping state is probably required to unregister conditionally.
    Since unregistering is safe (simply returns -ENOENT) when called after
    register fails. So I would think you can call unregister even when
    register fails.

    -- Shuah





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