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Support for exclusive activation of snapshots revealed some problems.
When snapshot is created, COW LV is activated first (for clearing) and
then it's transformed into snapshot's COW LV, but it has left the lock
for such LV active in cluster and this lock could not have been removed
from dlm, unless snapshot has been removed within same dlm session.
If the user tried to remove snapshot after rebooting node, the lock was
missing, and COW LV could not have been detached.
Patch modifes the approach in this way:
Always deactivate COW LV for clustered vg after clearing (so it's
activated again via imlicit snapshot activation rule when snapshot is activated).
When snapshot is removed, activate COW LV as independend LV, so the lock
will exist for such LV, but only when the snapshot is active.
Also add test case for testing snapshot removal after cluster reboot.
Patch fixes hidden problem with lvm metadata caching.
When the pretest was made, only the commited data have been cached back
since the call lv_info_by_lvid() triggers mda read operation.
However call of lv_suspend_if_active() also reads precommited metadata.
The problem is visible in this sequence of calls:
vg_write(), suspend_lv(), vg_commit(), resume_lv()
which may end with leaving outdated mda in lvm cache, since vg_write()
drops cached metadata and vg_commit() only transforms precommited
to commited metadata, but in the case of pretesting we have
no precommited mda available so the cache will continue to use
old metadata. This happens, when suspend LV is inactive.
Merging multiple config files together needs to know newest (highest)
timestamp of merged files. Persistent cache file is being used
only in case, the config file is older then .cache file.
Assign fid as the last step before returning VG.
Make the format reader for 'lvm1' and 'pool' equal to 'lvm2' format reader.
It has caused memory corruption to lvmetad as it later calls
destroy_instance() to allocated fid. This patch should fix problems
with crashing test lvmetad-lvm1.sh.
'lvchange' is used to alter a RAID 1 logical volume's write-mostly and
write-behind characteristics. The '--writemostly' parameter takes a
PV as an argument with an optional trailing character to specify whether
to set ('y'), unset ('n'), or toggle ('t') the value. If no trailing
character is given, it will set the flag.
Synopsis:
lvchange [--writemostly <PV>:{t|y|n}] [--writebehind <count>] vg/lv
Example:
lvchange --writemostly /dev/sdb1:y --writebehind 512 vg/raid1_lv
The last character in the 'lv_attr' field is used to show whether a device
has the WriteMostly flag set. It is signified with a 'w'. If the device
has failed, the 'p'artial flag has priority.
Example ("nosync" raid1 with mismatch_cnt and writemostly):
[~]# lvs -a --segment vg
LV VG Attr #Str Type SSize
raid1 vg Rwi---r-m 2 raid1 500.00m
[raid1_rimage_0] vg Iwi---r-- 1 linear 500.00m
[raid1_rimage_1] vg Iwi---r-w 1 linear 500.00m
[raid1_rmeta_0] vg ewi---r-- 1 linear 4.00m
[raid1_rmeta_1] vg ewi---r-- 1 linear 4.00m
Example (raid1 with mismatch_cnt, writemostly - but failed drive):
[~]# lvs -a --segment vg
LV VG Attr #Str Type SSize
raid1 vg rwi---r-p 2 raid1 500.00m
[raid1_rimage_0] vg Iwi---r-- 1 linear 500.00m
[raid1_rimage_1] vg Iwi---r-p 1 linear 500.00m
[raid1_rmeta_0] vg ewi---r-- 1 linear 4.00m
[raid1_rmeta_1] vg ewi---r-p 1 linear 4.00m
A new reportable field has been added for writebehind as well. If
write-behind has not been set or the LV is not RAID1, the field will
be blank.
Example (writebehind is set):
[~]# lvs -a -o name,attr,writebehind vg
LV Attr WBehind
lv rwi-a-r-- 512
[lv_rimage_0] iwi-aor-w
[lv_rimage_1] iwi-aor--
[lv_rmeta_0] ewi-aor--
[lv_rmeta_1] ewi-aor--
Example (writebehind is not set):
[~]# lvs -a -o name,attr,writebehind vg
LV Attr WBehind
lv rwi-a-r--
[lv_rimage_0] iwi-aor-w
[lv_rimage_1] iwi-aor--
[lv_rmeta_0] ewi-aor--
[lv_rmeta_1] ewi-aor--
Move common code for changing activation state from
vgchange and lvchange to one function.
Fix the order of checks - so we always implicitelly
activate snapshots and thin volumes in exclusive mode,
and we do not allow local deactivation for them.
New options to 'lvchange' allow users to scrub their RAID LVs.
Synopsis:
lvchange --syncaction {check|repair} vg/raid_lv
RAID scrubbing is the process of reading all the data and parity blocks in
an array and checking to see whether they are coherent. 'lvchange' can
now initaite the two scrubbing operations: "check" and "repair". "check"
will go over the array and recored the number of discrepancies but not
repair them. "repair" will correct the discrepancies as it finds them.
'lvchange --syncaction repair vg/raid_lv' is not to be confused with
'lvconvert --repair vg/raid_lv'. The former initiates a background
synchronization operation on the array, while the latter is designed to
repair/replace failed devices in a mirror or RAID logical volume.
Additional reporting has been added for 'lvs' to support the new
operations. Two new printable fields (which are not printed by
default) have been added: "syncaction" and "mismatches". These
can be accessed using the '-o' option to 'lvs', like:
lvs -o +syncaction,mismatches vg/lv
"syncaction" will print the current synchronization operation that the
RAID volume is performing. It can be one of the following:
- idle: All sync operations complete (doing nothing)
- resync: Initializing an array or recovering after a machine failure
- recover: Replacing a device in the array
- check: Looking for array inconsistencies
- repair: Looking for and repairing inconsistencies
The "mismatches" field with print the number of descrepancies found during
a check or repair operation.
The 'Cpy%Sync' field already available to 'lvs' will print the progress
of any of the above syncactions, including check and repair.
Finally, the lv_attr field has changed to accomadate the scrubbing operations
as well. The role of the 'p'artial character in the lv_attr report field
as expanded. "Partial" is really an indicator for the health of a
logical volume and it makes sense to extend this include other health
indicators as well, specifically:
'm'ismatches: Indicates that there are discrepancies in a RAID
LV. This character is shown after a scrubbing
operation has detected that portions of the RAID
are not coherent.
'r'efresh : Indicates that a device in a RAID array has suffered
a failure and the kernel regards it as failed -
even though LVM can read the device label and
considers the device to be ok. The LV should be
'r'efreshed to notify the kernel that the device is
now available, or the device should be 'r'eplaced
if it is suspected of failing.
...to not pollute the common and format-independent code in the
abstraction layer above.
The format1 pv_write has common code for writing metadata and
PV header by calling the "write_disks" fn and when rewriting
the header itself only (e.g. just for the purpose of changing
the PV UUID) during the pvchange operation, we had to tweak
this functionality for the format1 case and we had to assign
the PV the orphan state temporarily.
This patch removes the need for this format1 tweak and it calls
the write_disks with appropriate flag indicating whether this is
a PV write call or a VG write call, allowing for metatada update
for the latter one.
Also, a side effect of the former tweak was that it effectively
invalidated the cache (even for the non-format1 PVs) as we
assigned it the orphan state temporarily just for the format1
PV write to pass.
Also, that tweak made it difficult to directly detect whether
a PV was part of a VG or not because the state was incorrect.
Also, it's not necessary to backup and restore some PV fields
when doing a PV write:
orig_pe_size = pv_pe_size(pv);
orig_pe_start = pv_pe_start(pv);
orig_pe_count = pv_pe_count(pv);
...
pv_write(pv)
...
pv->pe_size = orig_pe_size;
pv->pe_start = orig_pe_start;
pv->pe_count = orig_pe_count;
...this is already done by the layer below itself (the _format1_pv_write fn).
So let's have this cleaned up so we don't need to be bothered
about any 'format1 special case for pv_write' anymore.
Add basic support for converting LV into an external origin volume.
Syntax:
lvconvert --thinpool vg/pool --originname renamed_origin -T origin
It will convert volume 'origin' into a thin volume, which will
use 'renamed_origin' as an external read-only origin.
All read/write into origin will go via 'pool'.
renamed_origin volume is read-only volume, that could be activated
only in read-only mode, and cannot be modified.
Reorder activation code to look similar for preload tree and
activation tree.
Its also give much better suppport for device stacking,
since now we also support activation of snapshot which might
be then used for other devices.
A new function (dm_tree_node_force_identical_table_reload) was added to
avoid the suppression of identical table reloads. This allows RAID LVs
to reload the on-disk superblock information that contains which devices
have failed and the bitmaps. If the failed device has returned, this has
the effect of restoring the device and initiating recovery. Without this
patch, the user had to completely deactivate their RAID LV and re-activate
it in order to restore the failed device. Now they simply need to
suspend and resume (which is done by 'lvchange --refresh').
The identical table suppression is only avoided if the LV is not PARTAIL
(i.e. all of it's devices can be seen and read by LVM) and the kernel
status of the array contains failed devices. In other words, the function
will only be called in the case where we may have success in restoring
a failed device in the array.
When there are missing PVs in a volume group, most operations that alter
the LVM metadata are disallowed. It turns out that 'vgimport' is one of
those disallowed operations. This is bad because it creates a circular
dependency. 'vgimport' will complain that the VG is inconsistent and that
'vgreduce --removemissing' must be run. However, 'vgreduce' cannot be run
because it has not been imported. Therefore, 'vgimport' must be one of
the operations allowed to change the metadata when PVs are missing. The
'--force' option is the way to make 'vgimport' happen in spite of the
missing PVs.
If zero metadata copies are used, there's no further recalculation of
PV alignment that happens when adding metadata areas to the PV and
which actually calculates the alignment correctly as a matter of fact.
So fix this for "PV without MDA" case as well.
Before this patch:
[1] raw/~ # pvcreate --dataalignment 8m --dataalignmentoffset 4m
--metadatacopies 1 /dev/sda
Physical volume "/dev/sda" successfully created
[1] raw/~ # pvs -o pv_name,pe_start
PV 1st PE
/dev/sda 12.00m
[1] raw/~ # pvcreate --dataalignment 8m --dataalignmentoffset 4m
--metadatacopies 0 /dev/sda
Physical volume "/dev/sda" successfully created
[1] raw/~ # pvs -o pv_name,pe_start
PV 1st PE
/dev/sda 8.00m
After this patch:
[1] raw/~ # pvcreate --dataalignment 8m --dataalignmentoffset 4m
--metadatacopies 1 /dev/sda
Physical volume "/dev/sda" successfully created
[1] raw/~ # pvs -o pv_name,pe_start
PV 1st PE
/dev/sda 12.00m
[1] raw/~ # pvcreate --dataalignment 8m --dataalignmentoffset 4m
--metadatacopies 0 /dev/sda
Physical volume "/dev/sda" successfully created
[1] raw/~ # pvs -o pv_name,pe_start
PV 1st PE
/dev/sda 12.00m
Also, remove a superfluous condition "pv->pe_start < pv->pe_align" in:
if (pe_start == PV_PE_START_CALC && pv->pe_start < pv->pe_align)
pv->pe_start = pv->pe_align ...
This part of the condition is not reachable as with the PV_PE_START_CALC,
we always have pv->pe_start set to 0 from the PV struct initialisation
(...the pv->pe_start value is just being calculated).
When a device fails, we may wish to replace those segments with an
error segment. (Like when a 'vgreduce --removemissing' removes a
failed device that happens to be a RAID image/meta.) We are then left
with images that we will eventually want to remove or replace.
This patch allows us to pull out these virtual "error" sub-LVs. This
allows a user to 'lvconvert -m -1 vg/lv' to extract the bad sub-LVs.
Sub-LVs with error segments are considered for extraction before other
possible devices so that good devices are not accidentally removed.
This patch also adds the ability to replace RAID images that contain error
segments. The user will still be unable to run 'lvconvert --replace'
because there is no way to address the 'error' segment (i.e. no PV
that it is associated with). However, 'lvconvert --repair' can be
used to replace the image's error segment with a new PV. This is also
the most appropriate way to do it, since the LV will continue to be
reported as 'partial'.
Currently it is impossible to remove a failed PV which has a RAID LV
on it. This patch fixes the issue by replacing the failed PV with an
'error' segment within the affected sub-LVs. Once there is no longer
a RAID LV using the PV, it can be removed.
Most often, it is better to replace a failed RAID device with a spare.
(You can use 'lvconvert --repair <vg>/<LV>' to accomplish that.)
However, if there are no spares in the volume group and none will be
added, it is useful to be able to removed the failed device.
Following patches address the ability to perform 'lvconvert' operations
on RAID LVs that contain sub-LVs composed of 'error' segments.
We have been using 'mirror_region_size' in lvm.conf as the default region
size for RAID logical volumes as well as mirror logical volumes. Since,
"raid" is more inclusive and representative than "mirror", I have changed
the name of this setting. We must still check for the old setting and warn
the user if we are overriding it with the new setting if both happen to be
present.
Instead of check for lv_is_active() for thin pool LV,
query the whole pool via new pool_is_active().
Fixes a problem when we cannot change discards settings
for active pool device where the actual layer for pool
device was inactive, but thin volumes using thin pool
have been active.
This internal function check for active pool device.
For cluster it checks every thin volume,
On the non-clustered VG we need to check just
for presence of -tpool device.
There are currently a few issues with the reporting done on RAID LVs and
sub-LVs. The most concerning is that 'lvs' does not always report the
correct failure status of individual RAID sub-LVs (devices). This can
occur when a device fails and is restored after the failure has been
detected by the kernel. In this case, 'lvs' would report all devices are
fine because it can read the labels on each device just fine.
Example:
[root@bp-01 lvm2]# lvs -a -o name,vg_name,attr,copy_percent,devices vg
LV VG Attr Cpy%Sync Devices
lv vg rwi-a-r-- 100.00 lv_rimage_0(0),lv_rimage_1(0)
[lv_rimage_0] vg iwi-aor-- /dev/sda1(1)
[lv_rimage_1] vg iwi-aor-- /dev/sdb1(1)
[lv_rmeta_0] vg ewi-aor-- /dev/sda1(0)
[lv_rmeta_1] vg ewi-aor-- /dev/sdb1(0)
However, 'dmsetup status' on the device tells us a different story:
[root@bp-01 lvm2]# dmsetup status vg-lv
0 1024000 raid raid1 2 DA 1024000/1024000
In this case, we must also be sure to check the RAID LVs kernel status
in order to get the proper information. Here is an example of the correct
output that is displayed after this patch is applied:
[root@bp-01 lvm2]# lvs -a -o name,vg_name,attr,copy_percent,devices vg
LV VG Attr Cpy%Sync Devices
lv vg rwi-a-r-p 100.00 lv_rimage_0(0),lv_rimage_1(0)
[lv_rimage_0] vg iwi-aor-p /dev/sda1(1)
[lv_rimage_1] vg iwi-aor-- /dev/sdb1(1)
[lv_rmeta_0] vg ewi-aor-p /dev/sda1(0)
[lv_rmeta_1] vg ewi-aor-- /dev/sdb1(0)
The other case where 'lvs' gives incomplete or improper output is when a
device is replaced or added to a RAID LV. It should display that the RAID
LV is in the process of sync'ing and that the new device is the only one
that is not-in-sync - as indicated by a leading 'I' in the Attr column.
(Remember that 'i' indicates an (i)mage that is in-sync and 'I' indicates
an (I)mage that is not in sync.) Here's an example of the old incorrect
behaviour:
[root@bp-01 lvm2]# lvs -a -o name,vg_name,attr,copy_percent,devices vg
LV VG Attr Cpy%Sync Devices
lv vg rwi-a-r-- 100.00 lv_rimage_0(0),lv_rimage_1(0)
[lv_rimage_0] vg iwi-aor-- /dev/sda1(1)
[lv_rimage_1] vg iwi-aor-- /dev/sdb1(1)
[lv_rmeta_0] vg ewi-aor-- /dev/sda1(0)
[lv_rmeta_1] vg ewi-aor-- /dev/sdb1(0)
[root@bp-01 lvm2]# lvconvert -m +1 vg/lv; lvs -a -o name,vg_name,attr,copy_percent,devices vg
LV VG Attr Cpy%Sync Devices
lv vg rwi-a-r-- 0.00 lv_rimage_0(0),lv_rimage_1(0),lv_rimage_2(0)
[lv_rimage_0] vg Iwi-aor-- /dev/sda1(1)
[lv_rimage_1] vg Iwi-aor-- /dev/sdb1(1)
[lv_rimage_2] vg Iwi-aor-- /dev/sdc1(1)
[lv_rmeta_0] vg ewi-aor-- /dev/sda1(0)
[lv_rmeta_1] vg ewi-aor-- /dev/sdb1(0)
[lv_rmeta_2] vg ewi-aor-- /dev/sdc1(0) ** Note that all the images currently are marked as 'I' even though it is
only the last device that has been added that should be marked.
Here is an example of the correct output after this patch is applied:
[root@bp-01 lvm2]# lvs -a -o name,vg_name,attr,copy_percent,devices vg
LV VG Attr Cpy%Sync Devices
lv vg rwi-a-r-- 100.00 lv_rimage_0(0),lv_rimage_1(0)
[lv_rimage_0] vg iwi-aor-- /dev/sda1(1)
[lv_rimage_1] vg iwi-aor-- /dev/sdb1(1)
[lv_rmeta_0] vg ewi-aor-- /dev/sda1(0)
[lv_rmeta_1] vg ewi-aor-- /dev/sdb1(0)
[root@bp-01 lvm2]# lvconvert -m +1 vg/lv; lvs -a -o name,vg_name,attr,copy_percent,devices vg
LV VG Attr Cpy%Sync Devices
lv vg rwi-a-r-- 0.00 lv_rimage_0(0),lv_rimage_1(0),lv_rimage_2(0)
[lv_rimage_0] vg iwi-aor-- /dev/sda1(1)
[lv_rimage_1] vg iwi-aor-- /dev/sdb1(1)
[lv_rimage_2] vg Iwi-aor-- /dev/sdc1(1)
[lv_rmeta_0] vg ewi-aor-- /dev/sda1(0)
[lv_rmeta_1] vg ewi-aor-- /dev/sdb1(0)
[lv_rmeta_2] vg ewi-aor-- /dev/sdc1(0)
** Note only the last image is marked with an 'I'. This is correct and we can
tell that it isn't the whole array that is sync'ing, but just the new
device.
It also works under snapshots...
[root@bp-01 lvm2]# lvs -a -o name,vg_name,attr,copy_percent,devices vg
LV VG Attr Cpy%Sync Devices
lv vg owi-a-r-p 33.47 lv_rimage_0(0),lv_rimage_1(0),lv_rimage_2(0)
[lv_rimage_0] vg iwi-aor-- /dev/sda1(1)
[lv_rimage_1] vg Iwi-aor-p /dev/sdb1(1)
[lv_rimage_2] vg Iwi-aor-- /dev/sdc1(1)
[lv_rmeta_0] vg ewi-aor-- /dev/sda1(0)
[lv_rmeta_1] vg ewi-aor-p /dev/sdb1(0)
[lv_rmeta_2] vg ewi-aor-- /dev/sdc1(0)
snap vg swi-a-s-- /dev/sda1(51201)
If there was a nested mountpoint inside an existing mount path,
blkdeactivate could fail to unmount such a mountpoint as it
needs to deactivate the deepest path first and continue upwards.
For example the simplest reproducer:
[root@rhel6-a ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 4G 0 disk
|-vg-lvol0 (dm-2) 253:2 0 32M 0 lvm /mnt/a
`-vg-lvol1 (dm-3) 253:3 0 32M 0 lvm /mnt/a/b
Before this patch:
[root@rhel6-a ~]# blkdeactivate -u
Deactivating block devices:
UMOUNT: unmounting vg-lvol0 (dm-2) mounted on /mnt/a
umount: /mnt/a: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))
UMOUNT: unmounting vg-lvol1 (dm-3) mounted on /mnt/a/b
LVM: deactivating Logical Volume vg/lvol1
(deactivation of vg/lvol0 is skipped as /mnt/a that is on lvol0
can't be unmounted - it still has /mnt/a/b as nested mountpoint!)
With this patch applied:
[root@rhel6-a ~]# blkdeactivate -u
Deactivating block devices:
UMOUNT: unmounting vg-lvol1 (dm-3) mounted on /mnt/a/b
UMOUNT: unmounting vg-lvol0 (dm-2) mounted on /mnt/a
LVM: deactivating Logical Volume vg/lvol0
LVM: deactivating Logical Volume vg/lvol1
===
Also, this patch contains a fix for processing mangled mount paths:
[root@rhel6-a ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 4G 0 disk
`-vg-lvol0 (dm-2) 253:2 0 32M 0 lvm /mnt/x y z
[root@rhel6-a ~]# lsblk -r
vg-lvol0 253:2 0 32M 0 lvm /mnt/x\x20y\x20z
(the mount path is mangled with \xNN that is visible in raw
lsblk output only and which is used in blkdeactive as well)
Before this patch:
[root@rhel6-a ~]# blkdeactivate -u
Deactivating block devices:
umount: /mnt/x\x20y\x20z: not found
After this patch applied:
[root@rhel6-a ~]# blkdeactivate -u
Deactivating block devices:
UMOUNT: unmounting vg-lvol0 (dm-2) mounted on /mnt/x\x20y\x20z
LVM: deactivating Logical Volume vg/lvol0
For reseting locale environment into significantly less memory
consuming version 'C' - use LC_ALL instead of LANG since it has
higher priority in locale settings.
Otherwise we may observe whole locale-archive which might be
over 100MB on i.e. Fedora systems locked in memory with
some daemons.
Add log/debug_classes to lvm.conf to allow debug messages to be
classified and filtered at runtime.
The dm_errno field is only used by log_error(), so I've redefined it
for log_debug() messages to hold the message class.
By default, all existing messages appear, but we can add categories that
generate high volumes of data, such as logging all traffic to/from
lvmetad.
We need to call sync_local_dev_names directly as pvscan uses
VG_GLOBAL lock and this one *does not* cause the synchronization
(sync_dev_names) to be called on unlock (VG_GLOBAL is not a real VG):
define unlock_vg(cmd, vol)
do { \
if (is_real_vg(vol)) \
sync_dev_names(cmd); \
(void) lock_vol(cmd, vol, LCK_VG_UNLOCK); \
} while (0)
Without this fix, we end up without udev synchronization for the
pvscan --cache (mainly for -aay that causes the VGs/LVs to be
autoactivated) and also udev synchronization cookies are then left
in the system since they're not managed properly (code before sets
up udev sync cookies, but we have to call dm_udev_wait at least once
after that to do the wait and cleanup).
Before, the pvscan --cache -aay was called on each ADD and CHANGE
uevent (for a device that is not a device-mapper device) and each CHANGE
event (for a PV that is a device-mapper device).
This causes troubles with autoactivation in some cases as CHANGE event
may originate from using the OPTION+="watch" udev rule that is defined
in 60-persistent-storage.rules (part of the rules provided by udev
directly) and it's used for all block devices
(except fd*|mtd*|nbd*|gnbd*|btibm*|dm-*|md* devices). For example, the
following sequence incorrectly activates the rest of LVs in a VG if one
of the LVs in the VG is being removed:
[root@rhel6-a ~]# pvcreate /dev/sda
Physical volume "/dev/sda" successfully created
[root@rhel6-a ~]# vgcreate vg /dev/sda
Volume group "vg" successfully created
[root@rhel6-a ~]# lvcreate -l1 vg
Logical volume "lvol0" created
[root@rhel6-a ~]# lvcreate -l1 vg
Logical volume "lvol1" created
[root@rhel6-a ~]# vgchange -an vg
0 logical volume(s) in volume group "vg" now active
[root@rhel6-a ~]# lvs
LV VG Attr LSize Pool Origin Data% Move Log
Cpy%Sync Convert
lvol0 vg -wi------ 4.00m
lvol1 vg -wi------ 4.00m
[root@rhel6-a ~]# lvremove -ff vg/lvol1
Logical volume "lvol1" successfully removed
[root@rhel6-a ~]# lvs
LV VG Attr LSize Pool Origin Data% Move Log
Cpy%Sync Convert
lvol0 vg -wi-a---- 4.00m
...so the vg was deactivated, then lvol1 removed, and we end up with
lvol1 removed (which is ok) BUT with lvol0 activated (which is wrong)!!!
This is because after lvol1 removal, we need to write metadata to the
underlying device /dev/sda and that causes the CHANGE event to be
generated (because of the WATCH udev rule set on this device) and this
causes the pvscan --cache -aay to be reevaluated.
We have to limit this and call pvscan --cache -aay to autoactivate
VGs/LVs only in these cases:
--> if the *PV is not a dm device*, scan only after proper device
addition (ADD event) and not with any other changes (CHANGE event)
--> if the *PV is a dm device*, scan only after proper mapping
activation (CHANGE event + the underlying PV in a state "just
activated")
