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Commit 3501f17fd0 enables a limited set
of metadata updates for partial LV/VGs when issuing lvchange or vgchange.
These tests verify those changes operate as intended.
A while back, the behavior of LVM changed from allowing metadata changes
when PVs were missing to not allowing changes. Until recently, this
change was tolerated by HA-LVM by forcing a 'vgreduce --removemissing'
before trying (again) to add tags to an LV and then activate it. LVM
mirroring requires that failed devices are removed anyway, so this was
largely harmless. However, RAID LVs do not require devices to be removed
from the array in order to be activated. In fact, in an HA-LVM
environment this would be very undesirable. Device failures in such an
environment can often be transient and it would be much better to restore
the device to the array than synchronize an entirely new device.
There are two methods that can be used to setup an HA-LVM environment:
"clvm" or "tagging". For RAID LVs, "clvm" is out of the question because
RAID LVs are not supported in clustered VGs - not even in an exclusively
activated manner. That leaves "tagging". HA-LVM uses tagging - coupled
with 'volume_list' - to ensure that only one machine can have an LV active
at a time. If updates are not allowed when a PV is missing, it is
impossible to add or remove tags to allow for activation. This removes
one of the most basic functionalities of HA-LVM - site redundancy. If
mirroring or RAID is used to replicate the storage in two data centers
and one of them goes down, a server and a storage device are lost. When
the service fails-over to the alternate site, the VG will be "partial".
Unable to add a tag to the VG/LV, the RAID device will be unable to
activate.
The solution is to allow vgchange and lvchange to alter the LVM metadata
for a limited set of options - --[add|del]tag included. The set of
allowable options are ones that do not cause changes to the DM kernel
target (like --resync would) or could alter the structure of the LV
(like allocation or conversion).
Compared to names, UUIDs can't be renamed once they are created
for a device. The 'mangle' command will just issue an error message
about a need for manual intervention in this case - reactivating the
device (remove + create) does the job as the defualt mangling mode
used is "auto" and that will assign a correct mangled form the UUID.
Just like we already have existing mangling support for
device-mapper names, we need exactly the same for device-mapper
UUIDs as their character whitelist is wider than what udev supports.
In case udev is used to create entries in /dev based on UUIDs
and these UUIDs contain characters not supported by udev,
we'll end up with incorrect /dev content for such devices.
So we need to mangle them to a form that is supported by udev.
The mangling used for UUIDs follows the mangling used for names
(that is already supported and used throughout). That means,
setting the name mangling mode via dm_set_name_mangling_mode
affects mangling used for UUIDs in exactly the same manner.
It would be useless to add a new and separate
dm_set_uuid_mangling_mode fn, we'll reuse existing interface.
(un)mangle_name -> (un)mangle_string
check_multiple_mangled_name_allowed -> check_multiple_mangled_string_allowed
Just for clarity as the same functions will be reused to (un)mangle dm UUIDs.
Separate original raid test and new raid10 test,
so the old could be tested on platforms without raid10 support.
Replace test-unfriendly `ls /dev/mapper` with dmsetup ls
The ExecStartPost with pvscan --cache in lvm2-lvmetad.service
is not needed now as this is called transparently within the
first LVM command that queries lvmetad.
