Re: [ptxdist] systemd: Using second offline update service beside rc-once in PTXDIST

[Michael Olbrich <m.olbrich@pengutronix.de>]

Hi,

On Fri, Jun 02, 2017 at 11:15:37AM +0000, Schenk, Gavin wrote:
> > > What do you think about using readlink in systemd-rc-once and just
> > > exit without error if /system-update does point to another location
> > > than /etc/rc-once?
> > > Another idea is to add a second service that doesn´t check
> > > /system-update either and use a after directive in its service file?
> > > Is this something we want a common solution for?
> > 
> > I think checking the link target for /system-update is a good solution.
> > This will keep things separated. But make sure the check is correct:
> > Currently /usr/sbin/enable-rc-once uses 'etc/rc.once.d' as link target
> > and /usr/lib/systemd/systemd-rc-once uses '/etc/rc.once.d' (in the
> > fallback case). I think that should be fixed, but both versions should
> > be accepted by systemd-rc-once.
> > 
> 
> Thank you for the fast feedback, I will send a patch.
> 
> Some Questions:
> Using readlink is ok? (additional dependency rc-once -> readlink ) 
> Is there anything more lightweight?

Not that I know. Note: if you use 'readlink -f' then the busybox version
has a option for this, so maybe:

	select BUSYBOX_FEATURE_READLINK_FOLLOW	if BUSYBOX_READLINK
	select COREUTILS			if !BUSYBOX_READLINK
	select COREUTILS_READLINK		if !BUSYBOX_READLINK

> Do we need this stuff configurable?

No. But I think we should have a sanity check. To avoid getting stuck in
the system-update.target: A service that is part of system-update.target
and starts the rescue target. rc-once.service and your service should both
be sorted 'Before' that service. If no other service starts a different
target we automatically fall into the rescue target.

Regards,
Michael

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