dev: detect mismatch between devices used and devices assumed for an LV

dev: detect mismatch between devices used and devices assumed for an LV

It's possible for an LVM LV to use a device during activation which
then differs from device which LVM assumes based on metadata later on.

For example, such device mismatch can occur if LVM doesn't have
complete view of devices during activation or if filters are
misbehaving or they're incorrectly set during activation.

This patch adds code that can detect this mismatch by creating
VG UUID and LV UUID index while scanning devices for device cache.

The VG UUID index maps VG UUID to a device list. Each device in the
list has a device layered above as a holder which is an LVM LV device
and for which we know the VG UUID (and similarly for LV UUID index).

We can acquire VG and LV UUID by reading /sys/block/<dm_dev_name>/dm/uuid.
So these indices represent the actual state of PV device use in
the system by LVs and then we compare that to what LVM assumes
based on metadata.

For example:

[0] fedora/~ # lsblk /dev/sdq /dev/sdr /dev/sds /dev/sdt
NAME         MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
sdq           65:0    0  104M  0 disk
|-vg-lvol0   253:2    0  200M  0 lvm
`-mpath_dev1 253:3    0  104M  0 mpath
sdr           65:16   0  104M  0 disk
`-mpath_dev1 253:3    0  104M  0 mpath
sds           65:32   0  104M  0 disk
|-vg-lvol0   253:2    0  200M  0 lvm
`-mpath_dev2 253:4    0  104M  0 mpath
sdt           65:48   0  104M  0 disk
`-mpath_dev2 253:4    0  104M  0 mpath

In this case the vg-lvol0 is mapped onto sdq and sds becauset this is
what was available and seen during activation. Then later on, sdr and
sdt appeared and mpath devices were created out of sdq+sdr (mpath_dev1)
and sds+sdt (mpath_dev2). Now, LVM assumes (correctly) that mpath_dev1
and mpath_dev2 are the PVs that should be used, not the mpath
components (sdq/sdr, sds/sdt).

[0] fedora/~ # pvs
  Found duplicate PV xSUix1GJ2SK82ACFuKzFLAQi8xMfFxnO: using /dev/mapper/mpath_dev1 not /dev/sdq
  Using duplicate PV /dev/mapper/mpath_dev1 from subsystem DM, replacing /dev/sdq
  Found duplicate PV MvHyMVabtSqr33AbkUrobq1LjP8oiTRm: using /dev/mapper/mpath_dev2 not /dev/sds
  Using duplicate PV /dev/mapper/mpath_dev2 from subsystem DM, ignoring /dev/sds
  WARNING: Device mismatch detected for vg/lvol0 which is accessing /dev/sdq, /dev/sds instead of /dev/mapper/mpath_dev1, /dev/mapper/mpath_dev2.
  PV                     VG     Fmt  Attr PSize   PFree
  /dev/mapper/mpath_dev1 vg     lvm2 a--  100.00m      0
  /dev/mapper/mpath_dev2 vg     lvm2 a--  100.00m      0