Dne 21. 02. 21 v 21:23 Martin Wilck napsal(a):
On Fri, 2021-02-19 at 23:47 +0100, Zdenek Kabelac wrote:
Right time is when switch is finished and we have rootfs with /usr
available - should be ensured by lvm2-monitor.service and it
dependencies.
While we're at it - I'm wondering why dmeventd is started so early. dm-
event.service on recent installments has only "Requires=dm-
event.socket", so it'll be started almost immediately after switching
root. In particular, it doesn't wait for any sort of device
initialization or udev initialization.
Hi
Dmeventd alone does not depend on lvm2 in any way - it's the lvm2 plugin which
then does all the 'scanning' for VGs/LVs and gets loaded when lvm2 connects to
monitoring socket. That's also why dmeventd belongs to dm subsystem.
Dmeventd is nothing else then a process to check DM devices periodically - and
can be used by i.e. dmraid or others...
So as such it doesn't need any devices - but it needs to be initialized early
so it can accept connections from tools like lvm2 and starts to monitor a
device without delaying command (as lvm2 wait for confirmation device is
monitored).
I've gone through the various tasks that dmeventd is responsible for,
and I couldn't see anything that'd be strictly necessary during early
boot. I may be overlooking something of course. Couldn't the monitoring
As said - during ramdisk boot - monitor shall not be used (AFAIK - dracut is
supposed to use disabled monitoring in it's modified copy of lvm.conf within
ramdisk)
But we want to switch to monitoring ASAP when we switch to rootfs - so the
'unmonitored' window is as small as possible - there are still same 'grey'
areas in the correct logic thought...
Zdenek
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