[linux-lvm] [PATCH] Detect systemd at run-time in 69-dm-lvm-metad.rules

[Julian Andres Klode]

On Tue, Jul 30, 2019 at 05:02:44PM +0200, Zdenek Kabelac wrote:
> Dne 25. 07. 19 v 20:49 Julian Andres Klode napsal(a):
> > systems might have systemd as their normal init systems, but
> > might not be using it in their initramfs; or like Debian, support
> > different init systems.
> > 
> > Detect whether we are running on systemd by checking for /run/systemd/system
> > and then change the behavior accordingly.
> > 
> 
> 
> Wouldn't it be better to simply disable compiling/using lvmetad on such systems ?

I don't see how this has anything to do with lvmetad. There is no lvmetad
anymore.

> HEAD of 2.03 already dropped lvmetad anyway.
> 
> Do you need any sort of autoactivation in ramdisk ?

Of course we need the PV to be scanned automatically so we can then find
the root partition. The root device finding is event-based, we have a tool
that listens to udev and waits for 30s for the device to appear, and relies
on the events being triggered correctly.

> There is probably higher complexity.
> 
> pvscan was not moved into systemd service just for fun - there have been at
> least 2 major mandatory points why  'pvscan' with autoactivation MUST NOT be
> executed from udev rule directly (udev timeout)
> 
> So the proposed patch must be NAC-ked as it is - as it probably causing way
> more troubles then it solves.

The alternative would be to disable the systemd integration entirely in
Debian and Ubuntu, as Debian requires support for non-systemd inits, and
Ubuntu requires event-based root device finding in initramfs. Surely that's
worse.

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