Filtering out LVs?

Filtering out LVs?

[Jun'ichi Nomura]

Hi,

LVM2 commands scan /dev for metadata read-in and validation.
By default, it includes DM devices.

On the other hand, LV deactivation checks its open count
and fails if it's open.

So there is a race that one of multiple vgchange instances prevents other;
"vgchange -an vg0" might fail to deactivate the VG if "vgchange -an vg1"
opens vg0/lv0 at the very time for scanning.

E.g. try this:
   From one console,
     # while true; do vgscan; done
   and from other console,
     # while true; do vgchange -ay $VG; vgchange -an $VG || break; done

While device filter can be configured to avoid LV devices,
and also someone may want to use LV as PV,
it seems inconvenient default behavior.

Does it make sense to add a filter to avoid LVs?
(It has to cope with multiple udev-oriented aliases...)

-- 
Jun'ichi Nomura, NEC Corporation

Filtering out LVs?

[Alasdair G Kergon]

On Tue, Mar 29, 2011 at 08:08:23PM +0900, Jun'ichi Nomura wrote:
> So there is a race that one of multiple vgchange instances prevents other;
> "vgchange -an vg0" might fail to deactivate the VG if "vgchange -an vg1"
> opens vg0/lv0 at the very time for scanning.
 
I'm inclined not to do anything about this at the moment, but to wait until
udev+new cache work is complete then revisit it if the problem hasn't
gone away.

Alasdair