Re: [lcd4linux] exec() question

[Michael R. <re...@eu...>]

Hi Lars,

>>> Does anyone know if you can get the exec() to execute
>>> once only instead of doing repeated executions?

>> But why the heck would one want to execute things only once???

> I'm working on a software RAID-1 solution with three S-ATA disks.
> One of these disks will be used as backup, i.e push the button
> (CF635), take out the disk, put another disk in, push another
> button, and voil=E1, you have a complete (and bootable) backup
> of your system on a separate disk, whilest the new disk is now
> being resynced. All with a running system (hotswap, no reboot).

Hey, this sounds cool! I will get a new server for my company this week
(a dual-core, so some of the SMP questions with lcd4linux will be
answered :-), and I'm planning to do something similar, but with two
harddisks only. So I'm a bit curious: how do you boot from and swap to
such a mirrored disk?

> I checked the mailinglist and couldn't find any plugin for
> /proc/mdstat, which I need in order to monitor the RAID.
> So I guess I'll have to write a plugin for /proc/mdstat.
This would be very very welcome :-) especially because I've got some
raid arrays up and running here (almost 1 TB for VDR :-)

> However, for prototyping I find the exec() function splendid.
> With the help of the exec() function and a simple shell-script,
> I have a running system where the CF635 display shows the
> RAID status. I even took care of stopping the underlying processes
> using a modified init.d script for start/stop of lcd4unix.
> So, in all fairness, it works well for me at least.

I've been thinking a bit about your issue. The problem with the exec()
plugin is that for timing reasons it's async by default. As a side
effect, the first call to exec() will never return a senseful result
(because the exec thread just forked off).

I see two solutions: modify the exec() plugin so it's thread terminates
after the first execution, but in this case you won't get a return
value. another way would be to force the exec() to be synchronous,
meaning not to fork. Maybe this could be implemented by using a negative
update parameter (while a update value of zero would mean a "one shot" ex=
ec.

> I also got the CF635 keypad working allright, thanks to
> Chris's patch for this the other week. However, I'm not
> sure how to execute a command (once!) using the keypad.
> Maybe there is another way that I don't know of?
> If not, I guess I'll have to look in to the code.
just curious again: What's chris's patch? (you are using CVS code, ain't
you?)

As I'm very very very busy with my real-life job at the moment, and my
son (who is six months old now! funny how time flies....) eats up the
rest of my spare time, I'm afraid I can't be of much help, especially
with coding.

If you feel familiar enough with coding for lcd4linux and patching the
repository, I could give you CVS developer access.


bye, Michael

--=20
Michael Reinelt <re...@eu...>
http://home.pages.at/reinelt
GPG-Key 0xDF13BA50
ICQ #288386781