Remove support for libvirt as multipass backend #4365

tobe2098 · 2025-09-17T12:13:04Z

The pull request removes from the multipass repo all components related to libvirt. This is part of the effort to restrict multipass to a single backend per platform.

There may still be driver specific logic that has been missed in the initial scan over the code.

Fixes #4364.

MULTI-1891

codecov · 2025-09-17T18:48:36Z

Codecov Report

❌ Patch coverage is 88.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.77%. Comparing base (bc0d111) to head (3fde1f7).
⚠️ Report is 57 commits behind head on main.

Files with missing lines	Patch %	Lines
src/daemon/daemon.cpp	81.81%	2 Missing ⚠️
src/utils/utils.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4365      +/-   ##
==========================================
+ Coverage   89.24%   89.77%   +0.52%     
==========================================
  Files         260      256       -4     
  Lines       17329    16872     -457     
==========================================
- Hits        15465    15146     -319     
+ Misses       1864     1726     -138

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tobe2098 · 2025-09-18T08:06:12Z

src/platform/backends/qemu/CMakeLists.txt

This should already be there, since daemon should link with libqemu.a. This absence caused problems when the CMakeLists.txt from libvirt, which contained daemon, was removed.

tests/linux/test_platform_linux.cpp

tests/test_cli_client.cpp

tests/test_daemon.cpp

tobe2098

Tested locally both the build and the snap, both seem to work fine. All google tests also passed.

tobe2098 · 2025-09-19T12:42:53Z

Additionally to all the changes directly related to libvirt I have found the following backend-dependant functions that could warrant a change/adaptation when LXD is removed:

In BaseVirtualMachineFactory:
- require_clone_support throws by default in virtual function, only not implemented in lxd and libvirt, otherwise does nothing. Can be removed entirely once both are gone.
- require_suspend_support does nothing by default in virtual function and only implemented in lxd to throw. Can be removed entirely once lxd is gone.
- require_snapshot_support throws by default in virtual function, only not implemented in lxd and libvirt, otherwise does nothing. Can be removed entirely once both are gone.
- clone_vm_impl is the same but the derived virtual functions do not have empty body. Cannot be removed.
In BaseVirtualMachine:
- require_snapshots_support, same as above.
- add_network_interface (not impl by libvirt) and make_native_mount (not impl by vbox and libvirt) throw by default but have implementations in the other backends, so cannot be removed.

Should I add a comment in the removable functions post LXD removal?

ricab · 2025-09-19T12:53:54Z

Yes please @tobe2098. Well spotted!

ricab · 2025-09-23T19:29:01Z

Hey Antoni, I noticed src/platform/backends/shared/qemu_img_utils/ while browsing code and started wondering: is anything in there used anywhere other than QEMU and libvirt? Possibly LXD? Would you mind having a look, to see if we could consolidate into just QEMU? Thanks!

tobe2098 · 2025-09-24T08:29:10Z

On it

Hey Antoni, I noticed src/platform/backends/shared/qemu_img_utils/ while browsing code and started wondering: is anything in there used anywhere other than QEMU and libvirt? Possibly LXD? Would you mind having a look, to see if we could consolidate into just QEMU? Thanks!

Both LXD and libvirt (ofc also QEMU) use the functions on that folder.
There is one particular function that is used by libvirt and qemu only, which could be moved in this PR to the qemu backend, but I think that we should move all of them once we remove LXD, since the rest will have to be moved then.

ricab · 2025-09-24T11:56:21Z

OK got it, that makes sense. I wouldn't object doing them together when removing LXD if you prefer. Up to you. You can also add TODO tags in the code if you think that's helpful.

sharder996

Looks good! Just a few nitpicks

docs/explanation/driver.md

src/client/cli/cmd/set.cpp

tests/test_daemon.cpp

src/platform/backends/qemu/CMakeLists.txt

Reintroduced test that was removed due to inaccurate comments.

Added comments earmarking the functions that can be removed once both libvirt and LXD have been removed as backends.

On LXD removal the qemu_img_utils can be moved to the qemu backend since it is the only caller.

The ARP cache displays IP addresses that have recently been translated from a MAC address. It can potentially contains stale IP addresses so we return the most recent IP address (assuming IP addresses are assigned in sequential order).

Ubuntu Core images initialize themselves in two stages separated by a guest system reboot. An IP address is assigned to the guest during the first phase even though networking is not fully initialized. We wait until a fresh IP is assigned and the guest signals it is ready by sending a response from a ping.

jimporter

This looks good to me.

tobe2098 self-assigned this Sep 17, 2025

tobe2098 commented Sep 18, 2025

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tobe2098 marked this pull request as ready for review September 18, 2025 15:34

tobe2098 force-pushed the backend/remove-libvirt branch 2 times, most recently from ea0e7aa to 49258bc Compare September 19, 2025 12:29

xmkg mentioned this pull request Sep 23, 2025

[test-platform-linux] Override libvirt.so properly #4339

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tobe2098 force-pushed the backend/remove-libvirt branch from e55c739 to 9a19181 Compare September 24, 2025 14:39

Sploder12 requested review from sharder996 and xmkg September 26, 2025 10:04

sharder996 requested changes Sep 29, 2025

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tobe2098 force-pushed the backend/remove-libvirt branch from f39edbb to 301d713 Compare September 29, 2025 15:19

tobe2098 requested a review from sharder996 October 1, 2025 07:37

sharder996 previously approved these changes Oct 1, 2025

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tobe2098 and others added 19 commits October 10, 2025 11:19

[ci] Fix linux-Clang.patch

103b75d

[lint] Remove trailing space

cc42a03

[tests] Reintroduce removed test

36d97e3

Reintroduced test that was removed due to inaccurate comments.

[docs] Fix conflict

8a542e9

[backend] Add LXD deprecation comments

e48eecc

Added comments earmarking the functions that can be removed once both libvirt and LXD have been removed as backends.

[backend] Add comment for posterior LXD removal

152577b

On LXD removal the qemu_img_utils can be moved to the qemu backend since it is the only caller.

[backend-utils] Return most recent IP address

ba5d237

The ARP cache displays IP addresses that have recently been translated from a MAC address. It can potentially contains stale IP addresses so we return the most recent IP address (assuming IP addresses are assigned in sequential order).

[backend-utils] Log discovered IP addresses

3809a3c

[utils] Use shared utils function to ping guest

9e6e516

[utils] Return immediately upon receiving response

7613af0

[utils] Expand comment to describe stale cache

9a58de3

[tests] Expand test suite for new logic

2b89bba

[utils] Add missing include

233b698

[utils] Cleanup var names, etc

9ab9f6a

[utils] Reorganize util function can_reach_gateway

994df2c

[utils] Remove unnecessary include

adbb463

[docs] Remove commented line

32f1989

[cli] Remove parenthesis in src/cli/set.cpp

3fde1f7

tobe2098 dismissed sharder996’s stale review via 3fde1f7 October 10, 2025 09:19

tobe2098 force-pushed the backend/remove-libvirt branch from 301d713 to 3fde1f7 Compare October 10, 2025 09:19

tobe2098 requested a review from sharder996 October 10, 2025 12:31

sharder996 approved these changes Oct 13, 2025

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jimporter approved these changes Oct 14, 2025

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tobe2098 added this pull request to the merge queue Oct 14, 2025

tobe2098 removed this pull request from the merge queue due to a manual request Oct 14, 2025

tobe2098 added this pull request to the merge queue Oct 14, 2025

Merged via the queue into main with commit f42cf65 Oct 14, 2025
21 of 22 checks passed

tobe2098 deleted the backend/remove-libvirt branch October 14, 2025 09:43

Remove support for libvirt as multipass backend #4365

Remove support for libvirt as multipass backend #4365

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