Description of problem:

The built-in lvm filter-mpath detects and ignores multipath component devices, but sometimes component devs can get through the filter and be seen by lvm commands [1].

When this happens, lvm sees the same PV on different devices and warns about "duplicate PVs".  More critically, lvm activation commands will not activate LVs when these duplicate PVs are seen.  This often leads to a boot failure when the root LV fails to be activated (or some other LV required for boot.)

LVM now has access to device wwids, and this can be used to detect and eliminate multipath components if they happen to get through the filter.  This means that cases of failed multipath component detection should not longer prevent lvm from operating normally.

upstream commit:
https://sourceware.org/git/?p=lvm2.git;a=commit;h=212b1fc529a7d550c49f32cb7cbecb017ceb35b0

[1] filter-mpath has traditionally relied on the kernel sysfs info from dm multipath devs to detect components, but sometimes the multipath device is not set up when needed, causing the components to get through the filter.  More recently the filter began using /etc/multipath/wwids as a secondary method of detecting a component device.  If both of these methods fail, then the new wwid comparison of duplicate PVs described above will resolve the problem (although it occurs later in the command than the filter, so is somewhat less efficient because lvm will read the component devs prior to eliminating them.)

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