Add s6 notify support to mdevd plugin

[hongkongkiwi]

Could you please add S6 readyness support to mdevd:

https://github.com/troglobit/finit/blob/master/plugins/mdevd.c#L41

#define MDEVD_ARGS   "-C -O 4 -D %n"

https://github.com/troglobit/finit/blob/master/plugins/mdevd.c#L87

    if (debug)
        snprintf(line, sizeof(line), "[S12345789] cgroup.system notify:s6 pid:!%s @%s:%s %s -v3 %s -- %s",
             MDEVD_DAEMONPIDFILE, MDEVD_DAEMONUSER, MDEVD_DAEMONGROUP, cmd, MDEVD_ARGS, MDEVD_DESC);
    else
        snprintf(line, sizeof(line), "[S12345789] cgroup.system notify:s6 pid:!%s @%s:%s %s %s -- %s",
             MDEVD_DAEMONPIDFILE, MDEVD_DAEMONUSER, MDEVD_DAEMONGROUP, cmd, MDEVD_ARGS, MDEVD_DESC);

[troglobit]

Ah yes, thanks for reminding me! I knew there was something obvious I had forgot ...

[troglobit]

Pending #328, this issue and plugin may be completely dropped in favor of a simple .conf file.

[hongkongkiwi]

Whats the thinking to drop this as a plugin? I thought the idea was to get it to startup extremely early before anything else is loaded.

[troglobit]

The plugin and the new notify features are logically equivalent to the two .conf lines in #328. Since mdevd runs as a monitored service, as compared to plain BusyBox mdev, it will have to start as regular tasks and services do in runlevel S. In many cases I'd recommend going with just mdev, which would be quicker, but you seem to have built a lot of logic around mdevd.

[troglobit]

Andy did you see my reply, understand the reasoning, and are OK with my removing mdevd as a plugin (and softdep in other plugins) in Finit?

This task and the /dev conditions support are the only two remaining features for the v4.4 release, and I'd really like to finalize it this month. Because the next 6-12 months I will be extremely busy in a customer project where I'll be needing the v4.4 release.

[hongkongkiwi]

I'm having an issue with this, but the issue doesn't make any sense to me at present (mdevd will crash the first time it runs then it will run fine), perhaps we leave it as is? Maybe instead we fix the issue where we don't want to build either plugin #331 and it can be switched off and added to the config manually for 4.4.

Whats strange is it originally worked, now it doesn't, it's most likely my system, but probably no rush to remove this right as it's a compile time option anywho.

[troglobit]

Very odd, the two ways of starting mdevd+coldplug (plugin and .conf) are equivalent. I can check if I can see the same issue as you. Otherwise I'd rather remove the plugin.

It was added in this release cycle, so a lot easier to revert it now, because leaving it in means it's a supported feature and someone else will start using it as well. Meaning I can never really remove it ...

Removing it now is a lot easier than adding a lot of extra checks and do manual tests to fix #331 in a manner that actually makes those plugins not check if mdevd is disabled.

[troglobit]

Spent a while trying to reproduce your issue, without success I'm afraid. Stable as a rock here, and I might add, it runs at the same point in time compared to the plugin.

[hongkongkiwi]

Thanks for looking into it, go ahead and make the change. There might be something else strange going on.

[troglobit]

Alright, thank you. Hope you find the root cause of your problems!

[hongkongkiwi]

For the new S6 mechanism, how long does the finit wait for the s6 notify signal before restarting a service? Can this delay be modified?

[troglobit]

Not sure I'm following here, there is no such mechanism to restart if there is no readiness notification.

[troglobit]

Readiness notification added to plugin in 180859a and was subsequently dropped in f6bfbc8, as discussed previously.