Rename ring buffer to com.canonical.lxd

[MusicDin]

This PR updates the name of ring buffer from org.linuxcontainers.lxd to com.canonical.lxd.

With this change in place, restart of existing VMs will be required. Otherwise, (old) lxd-agent will write data to the org.linuxcontainers.lxd qemu serial device that is not connected to the new ring buffer from which lxd server will try to read. After VM is restarted, new lxd-agent will be copied from the shared host filesystem to the VM.

Fixes #12149

[mihalicyn]

Looks good to me!

And also thanks for adding a great explanatory comments.

[mihalicyn]

We still need to test this very-very carefully to be 100% that nothing was missed.

[simondeziel]

LGTM with some tiny nitpicks.

[tomponline]

@simondeziel @MusicDin would we be able to add some tests to lxd-ci that would check that the agent is working on an older image (e.g. jammy assuming the SRU won't go through) is working with the newer LXD?

And also that the agent is working in an image for a newer version of Ubuntu (once our changes land in lxd-agent-loader package) on an older (5.0/stable) LXD?

[tomponline]

LGTM thanks!

What was the outcome of the test to statefully restore a VM running an older lxd-agent that talks to the older serial device?

[MusicDin]

Steps that I did (Also see the spec where I tried to document this https://discourse.ubuntu.com/t/rename-lxd-ring-buffer-to-com-canonical-lxd/40499):

$ lxc launch ubuntu:22.04 v1 --vm
$ lxc snapshot v1 mysnap --stateful

# >> Upgrade LXD

# This will work, because VM state is not recovered.
$ lxc restore v1 mysnap
$ lxc start v1

# This will NOT work, because old LXD agent is restored as well and it is not able
# to communicate with the LXD server through a common ring buffer.
$ lxc restore v1 mysnap --stateful
Error: Failed restoring state from "/var/snap/lxd/common/lxd/virtual-machines/v1/state": Monitor is disconnected

[tomponline]

Steps that I did (Also see the spec where I tried to document this https://discourse.ubuntu.com/t/rename-lxd-ring-buffer-to-com-canonical-lxd/40499):

$ lxc launch ubuntu:22.04 v1 --vm
$ lxc snapshot v1 mysnap --stateful

# >> Upgrade LXD

# This will work, because VM state is not recovered.
$ lxc restore v1 mysnap
$ lxc start v1

# This will NOT work, because old LXD agent is restored as well and it is not able
# to communicate with the LXD server through a common ring buffer.
$ lxc restore v1 mysnap --stateful
Error: Failed restoring state from "/var/snap/lxd/common/lxd/virtual-machines/v1/state": Monitor is disconnected

Hrm, are you sure the failure to restore the snapshot was due to the ring buffer? Did you get an error from the qemu logs?

[MusicDin]

Good point, need to verify that

[MusicDin]

Hrm, are you sure the failure to restore the snapshot was due to the ring buffer? Did you get an error from the qemu logs?

You were right Tom, my assumption was wrong. According to @mihalicyn, the issue is related to non-existing state of the new serial device.

Here is the instance log:

qemu-system-x86_64: Failed to load virtio-console:virtio
qemu-system-x86_64: error while loading state for instance 0x0 of device '0000:00:01.0:00.5/virtio-console'
qemu-system-x86_64: load of migration failed: Invalid argument

[tomponline]

OK thats fine then as we wont need to consider restoring an actively running older agent.