Since udev will probe block devices it is advisable to hold a lock
on the device when modifying its partition table or the superblock
of the filesystem (see [1]). osbuild loopback devices do support
this via the `lock` option. Set this option for all operation that
involve changing block device "metadata" that could potentionally
race with udev, such as sfdisk, mkfs, creating a luks2 container
and creating LVM2 volume groups and logical volumes.
NB: osbuild also has its own device inhibition logic to prevent
udev/lvm2 from auto activating devices and in general to limit the
interaction between the host and devices used by osbuild. See [2]
for more information.
NB: this also locks the loopback device in situation where we the
it is strickly not the right thing to do, e.g. when creating a fs
on a logical voume that is located on a loopback device, since in
this case the device we would need to lock is the logical volume.
Sadly, LVM/DM devices are exempt from block device locking. But,
due to a bug in osbuild < 50, the udev inhibitor does *not* work
for loopback devices and therefore we have to use the actual lock
to preven LVM device auto-activation via `69-dm-lvm-metad.rules`.
The change was implemented by adding a new boolean to `getDevices`
indicating if the loopback device should be locked or not. Once
we depend on osbuild 50 we can change the logic in `getDevices`
to only lock the loopback device if the number of devices is one,
i.e. we are working directly on the loopback device.
[1] https://systemd.io/BLOCK_DEVICE_LOCKING/
[2] /usr/lib/udev/rules.d/10-osbuild-inhibitor.rules
Add new helper functions that will return the necessary stages to
prepare a disk image, i.e. take care of creating the raw image
file, partitioning it, creating the devices on it (LUKS2, LVM2),
and formatting all the file systems: `GenImageStagesPrepare`.
Additionally, some partition layouts require some post-processing,
e.g. LVM2 where the volume group needs to be renamed "offline".
For this the `GenImageFinishStages` was added.
Co-Authored-By: Achilleas Koutsou <achilleas@koutsou.net>
