[linux-lvm] LVM autoactivation and udev

[Martin Wilck <mwilck@suse.com>]

Hi David, hi Peter,

we have recently updated LVM2 on openSUSE Factory, and are using the
autoactivation feature now. We also use
'external_device_info_source="udev"' by default, because according to
our experience it is the only way to make LVM device detection work
reliably with multipath devices.

With these settings, we see lots of "Udev database has incomplete
information about device ..." messages:

> [   12.377563] apollon systemd-udevd[810]: sda5: Processing device (SEQNUM=2787, ACTION=add)
> [   12.412723] apollon systemd-udevd[810]: sda5: /usr/lib/udev/rules.d/69-dm-lvm.rules:82 Importing properties from results of '/usr/sbin/lvm pvscan --cache --listvg --checkcomplete --vgonline --autoactivation event --udevoutput --journal=output /dev/sda5'
> [   12.412767] apollon systemd-udevd[810]: sda5: Starting '/usr/sbin/lvm pvscan --cache --listvg --checkcomplete --vgonline --autoactivation event --udevoutput --journal=output /dev/sda5'
> [   12.413041] apollon systemd-udevd[810]: Successfully forked off '(spawn)' as PID 882.
> [   12.419458] apollon lvm[882]: Udev database has incomplete information about device /dev/sda5.

This is no surprise, because 69-dm-lvm.rules contains

IMPORT{program}="/usr/sbin/lvm pvscan --cache --listvg --checkcomplete --vgonline --autoactivation event --udevoutput --journal=output $env{DEVNAME}"
ENV{LVM_VG_NAME_COMPLETE}=="?*", RUN+="/usr/bin/systemd-run --no-block --property DefaultDependencies=no --unit lvm-activate-$env{LVM_VG_NAME_COMPLETE} (LVM_EXEC)/lvm vgchange -aay --autoactivation event $env{LVM_VG_NAME_COMPLETE}"

These rules are executed by udev while it is processing an "add" event
for a PV. At that time, the udev data base doesn't contain an entry for
this PV yet, because the entry is added only after the uevent is fully
processed.

Shouldn't "pvscan" be run in a RUN+= statement instead? Obviously if we
do this, the lvm-activate-$VG unit must be started in some other way
(e.g. by calling systemd-run directly from pvscan).

In the cases we have observed so far, the VGs were assembled correctly
despite these warnings. We aren't certain if this was by luck only. In
any case, the messages irritate users.

Or are we getting this completely wrong, and the new autoactivation
feature should not be used with external_device_info_source="udev" at
all? If that's the case, how is multipath component detection supposed
to work?

Regards,
Martin

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