** Description changed:
+ [ Impact ]
+
+ PackageKit's APT backend still uses APT's legacy ("old") dependency solver,
+ whereas the APT command-line tools have switched to the new solver 3.0 by
+ default. This inconsistency causes PackageKit (and therefore tools built on
+ top of it, such as GNOME Software / App Center and `pkgcli`) to compute
+ different, worse solutions than `apt` for the same operation.
+
+ The most visible symptom is that PackageKit silently drops Recommends when
+ resolving installs that involve a virtual package provided by more than one
+ package. For example:
+
+ pkgcli install virt-manager
+
+ does NOT pull in the recommended `libvirt-daemon-system`, leaving the user
+ with a non-functional local virtualization stack, while:
+
+ sudo apt install virt-manager
+
+ correctly installs `libvirt-daemon-system` and its dependencies.
+
+ Root cause: the chain
+ virt-manager Recommends libvirt-daemon-system
+ libvirt-daemon-system Depends libvirt-daemon-driver-qemu
+ libvirt-daemon-driver-qemu Depends qemu-kvm | qemu-system
+ hits a virtual package (`qemu-kvm`) that is provided by both
+ `qemu-system-x86` (GA stack) and `qemu-system-x86-hwe` (HWE stack). The old
+ solver first tries the HWE provider, generates a conflict by mixing stacks,
+ and then resolves the conflict by simply dropping the Recommends instead of
+ choosing the correct GA provider. The new solver 3.0 handles this case
+ correctly, matching the behaviour of the `apt` CLI.
+
+ [ Test Plan ]
+
+ On an up-to-date Ubuntu system with the affected packagekit version:
+
+ 1. Ensure neither virt-manager nor libvirt-daemon-system is installed:
+ dpkg -l virt-manager libvirt-daemon-system
+ 2. Run a simulated install via PackageKit:
+ pkgcli install virt-manager
+ (or via GNOME Software / App Center).
+ 3. Observe the list of packages to be installed.
+
+ Expected result WITHOUT the fix:
+ `libvirt-daemon-system` is NOT in the install set; only the strictly
+ required dependencies are pulled in. The result differs from
+ `apt install virt-manager`.
+
+ Expected result WITH the fix:
+ `libvirt-daemon-system` (and the rest of the GA QEMU/virt stack, e.g.
+ `libvirt-daemon-driver-qemu`, `qemu-system-x86`, `qemu-system-common`,
+ `qemu-system-gui`, ...) IS included, matching the output of
+ `apt install virt-manager`.
+
+ [ Where problems could occur ]
+
+ The change switches the APT backend to solver 3.0 by setting
+ `APT::Solver` to "3.0" during backend initialization (guarded by an
+ `APT_PKG_ABI >= 700` check, so it only takes effect where solver 3.0 is
+ available). Because this changes the dependency-resolution engine used by
+ PackageKit, any regression would manifest as PackageKit computing different
+ install/remove/update solutions than before:
+
+ - Transactions that previously succeeded could in theory fail to find a
+ solution, or vice-versa, though solver 3.0 is generally strictly better
+ at producing correct results and is already the default for the `apt`
+ CLI, so PackageKit is simply being aligned with well-tested behaviour.
+
+
+ [ Other Info ]
+
+ * Fix forwarded upstream:
+ https://github.com/PackageKit/PackageKit/pull/983
+
+ * I run an extensive testing of the proposed packagekit on a set of 140
packages related to the virt stack (reverse dependencies, virt packages). And
the list of installed packages are identical between packagekit and APT.
+ This give us the confidence that the transition to Solver 3.0 does not
+ break anything.
+
+ ---------
Fully updated Ubuntu 26.04 LTS system, packagekit 1.3.4-3.
Originally reported as an App Center issue
(https://github.com/ubuntu/app-center/issues/2092), but "pkgcli install"
has the same problem.
When installing a deb package (from Universe, but it probably does not
matter), only its "required" dependencies are installed, not
"recommended" ones.
You can test this yourself by running:
$ pkgcli install virt-manager
# does not install "libvirt-daemon-system", resulting in a non-working local
virtualization
vs
$ sudo apt install virt-manager
# also installs "libvirt-daemon-system" and everything works fine
** Changed in: libvirt (Ubuntu Resolute)
Assignee: (unassigned) => Hector CAO (hectorcao)
** No longer affects: libvirt (Ubuntu Resolute)
** No longer affects: libvirt (Ubuntu Stonking)
** Changed in: packagekit (Ubuntu Resolute)
Assignee: (unassigned) => Hector CAO (hectorcao)
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https://bugs.launchpad.net/bugs/2148469
Title:
`libvirt-daemon-driver-qemu` prefers `qemu-system-x86-hwe` to satisfy
`qemu-kvm | qemu-system` dependency
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