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With latest changes in the udev, some deprecated functions were removed
from libudev amongst which there was the "udev_get_dev_path" function
we used to compare a device directory used in udev and directore set in
libdevmapper. The "/dev" is hardcoded in udev now (udev version >= 183).
Amongst other changes and from packager's point of view, it's also
important to note that the libudev development library ("libudev-devel")
could now be a part of the systemd development library ("systemd-devel")
because of the udev + systemd merge.
Support has many limitations and lots of FIXMEs inside,
however it makes initial task when user creates a separate LV for
thin pool data and thin metadata already usable, so let's enable
it for testing.
Easiest API:
lvconvert --chunksize XX --thinpool data_lv metadata_lv
More functionality extensions will follow up.
TODO: Code needs some rework since a lot of same code is getting copied.
When mirrors are up-converted, a transient mirror layer is put in so that
only the new devices are sync'ed. That transient layer must carry the tags
of the original mirror LV, otherwise it will fail to activate when activation
is regulated by lvm.conf:activation/volume_list. The conversion would then
fail.
The fix is to do exactly the same thing that is being done for linear ->
mirror converting (lib/metadata/mirror.c:_init_mirror_log()). We copy the
tags temporarily for the new LV and remove them after the activation.
Snapshots of RAID logical volumes are allowed (including "raid1"). However,
snapshots of "mirror" logical volumes has been disallowed due to unsolvable
issues inherent to the design. The fact that mirroring (dm-raid1.c) must
stop all I/O as the result of a failure and wait for userspace intervention
can lead to a circular dependency if userspace is simultaneously waiting for
snapshots (on mirrors) to make an I/O update before proceeding.
Various snapshot on mirror tests have been removed as a result.
Looking at the code in cmirrord/local.c, we can see the various different
request types handled in different ways. Some information that is non-changing
does not need to go around the cluster and can be short-circuited. For
example, once the cluster mirror is in-sync, it is pointless to continue
sending that query around the cluster. We can save network bandwidth and reply
directly back to the kernel. When it comes to status information, there are
two types 'TABLE' and 'INFO'. The 'TABLE' information never changes and
belongs to the group of requests that can be safely short-circuited. The
'STATUS' information can change - and will change if a device fails. Thus it
cannot be short-circuited, but this is exactly what was found. The 'STATUS'
information request was being short-circuited and therefore never reporting the
failure condition to anyone other than the "server" that experienced it
directly.
