29.11.2021 03:36, Michał Mirosław пишет:

On Mon, Nov 29, 2021 at 12:53:51AM +0300, Dmitry Osipenko wrote:

quoted

29.11.2021 00:17, Michał Mirosław пишет:

quoted

quoted

I'm having trouble with parsing this comment. Could you please try to
rephrase it? I don't see how you could check whether power-off handler
is available if you'll mix all handlers together.

If notify_call_chain() would be fixed to return NOTIFY_OK if any call
returned NOTIFY_OK, then this would be a clear way to gather the
answer if any of the handlers will attempt the final action (reboot or
power off).

Could you please show a code snippet that implements your suggestion?

A rough idea is this:

 static int notifier_call_chain(struct notifier_block **nl,
 			       unsigned long val, void *v,
 			       int nr_to_call, int *nr_calls)
 {
-	int ret = NOTIFY_DONE;
+	int ret, result = NOTIFY_DONE;
 	struct notifier_block *nb, *next_nb;
 
 	nb = rcu_dereference_raw(*nl);
 
 	while (nb && nr_to_call) {
...
 		ret = nb->notifier_call(nb, val, v);
+
+		/* Assuming NOTIFY_STOP-carrying return is always greater than non-stopping one. */
+		if (result < ret)
+			result = ret;
... 
 	}
-	return ret;
+	return result;
 }

Then:

bool prepare_reboot()
{
	int ret = xx_notifier_call_chain(&shutdown_notifier, PREPARE_REBOOT, ...);
	return ret == NOTIFY_OK;
}

And the return value would signify whether the reboot will be attempted
when calling the chain for the REBOOT action. (Analogously for powering off.)

If you started to execute call chain, then you began the power-off /
restart sequence, this is a point of no return. Sorry, I still don't
understand what you're trying to achieve.

The approach of having separate call chains is simple and intuitive, I
don't see reasons to change it.