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osbuild2: lock loopback devices during sfdisk, mkfs

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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
This commit is contained in:
Christian Kellner 2022-02-28 13:19:28 +01:00
parent 19e7890f63
commit 9e5b265a58
112 changed files with 742 additions and 371 deletions
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12
test/data/manifests/centos_9-aarch64-openstack-boot.json
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@ -951,7 +951,8 @@
"device": {
"type": "org.osbuild.loopback",
"options": {
"filename": "disk.img"
"filename": "disk.img",
"lock": true
}
}
}
@ -967,7 +968,8 @@
"options": {
"filename": "disk.img",
"start": 2048,
"size": 409600
"size": 409600,
"lock": true
}
}
}
@ -984,7 +986,8 @@
"options": {
"filename": "disk.img",
"start": 411648,
"size": 1024000
"size": 1024000,
"lock": true
}
}
}
@ -1001,7 +1004,8 @@
"options": {
"filename": "disk.img",
"start": 1435648,
"size": 6952927
"size": 6952927,
"lock": true
}
}
}