image-info: Add workaround for listing services by status

`image-info` tools parses output of `systemctl list-unit-files` run on a
different tree (with `--root` option), to determine the list of enabled
and disabled services on the inspected image. However since Fedora 33
(and presumably since systemd v246), the output of `systemctl
list-unit-files` changed. Some units previously reported as "enabled" or
"disabled" are now reported as "alias", which means, that they are just
a symlink to a different unit.

There is no systemd command, that would take an "alias" unit and would
report its state as "enabled" or "disabled" and could run on a different
tree (with "--root" option).

To make the list of reported services in the given state consistent on
systems with older and new (v246+) systemd version, check all "alias"
units and append them to the list of services with a specific status,
if their target is also listed in in the list.

Example of the `systemctl list-unit-files` output change:

~]# rpm -q systemd
systemd-246.6-3.fc33.x86_64
~]# systemctl list-unit-files ctrl-alt-del.target
UNIT FILE           STATE VENDOR PRESET
ctrl-alt-del.target alias -

~]# rpm -q systemd
systemd-245.8-2.fc32.x86_64
~]# systemctl list-unit-files ctrl-alt-del.target
UNIT FILE           STATE   VENDOR PRESET
ctrl-alt-del.target enabled disabled

This change makes it possible to produce consistent output for an
inspected image, regardless if the `image-info` tool is run on Fedora
32, Fedora 33 or RHEL-8.

Also regenerate all Fedora 33 test cases, since this commit changes the
content of produced list of enabled / disabled services since Fedora 33.
The list is now consistent with what would be produced by `image-info`
for an image on older Fedora (e.g. 32) or RHEL-8.

Signed-off-by: Tomas Hozza <thozza@redhat.com>

tools/image-info

@@ -134,9 +134,6 @@ def parse_unit_files(s, expected_state):
             continue
         r.append(unit)
 
-    # deduplicate and sort
-    r = list(set(r))
-    r.sort()
     return r
 
 
@@ -265,8 +262,69 @@ def rpm_packages(tree, is_ostree):
     return list(sorted(pkgs))
 
 
+@contextlib.contextmanager
+def change_root(root):
+    real_root = os.open("/", os.O_RDONLY)
+    try:
+        os.chroot(root)
+        yield None
+    finally:
+        os.fchdir(real_root)
+        os.chroot(".")
+        os.close(real_root)
+
+
 def read_services(tree, state):
-    return subprocess_check_output(["systemctl", f"--root={tree}", "list-unit-files"], (lambda s: parse_unit_files(s, state)))
+    services_state = subprocess_check_output(["systemctl", f"--root={tree}", "list-unit-files"], (lambda s: parse_unit_files(s, state)))
+
+    # Since systemd v246, some services previously reported as "enabled" /
+    # "disabled" are now reported as "alias". There is no systemd command, that
+    # would take an "alias" unit and report its state as enabled/disabled
+    # and could run on a different tree (with "--root" option).
+    # To make the produced list of services in the given state consistent on
+    # pre/post v246 systemd versions, check all "alias" units and append them
+    # to the list, if their target is also listed in 'services_state'.
+    if state != "alias":
+        services_alias = subprocess_check_output(["systemctl", f"--root={tree}", "list-unit-files"], (lambda s: parse_unit_files(s, "alias")))
+
+        for alias in services_alias:
+            # The service may be in one of the following places (output of
+            # "systemd-analyze unit-paths", it should not change too often).
+            unit_paths = [
+                "/etc/systemd/system.control",
+                "/run/systemd/system.control",
+                "/run/systemd/transient",
+                "/run/systemd/generator.early",
+                "/etc/systemd/system",
+                "/run/systemd/system",
+                "/run/systemd/generator",
+                "/usr/local/lib/systemd/system",
+                "/usr/lib/systemd/system",
+                "/run/systemd/generator.late"
+            ]
+
+            with change_root(tree):
+                for path in unit_paths:
+                    unit_path = os.path.join(path, alias)
+                    if os.path.exists(unit_path):
+                        real_unit_path = os.path.realpath(unit_path)
+                        # Skip the alias, if there was a symlink cycle.
+                        # When symbolic link cycles occur, the returned path will
+                        # be one member of the cycle, but no guarantee is made about
+                        # which member that will be.
+                        if os.path.islink(real_unit_path):
+                            continue
+
+                        # Append the alias unit to the list, if its target is
+                        # already there.
+                        if os.path.basename(real_unit_path) in services_state:
+                            services_state.append(alias)
+
+    # deduplicate and sort
+    services_state = list(set(services_state))
+    services_state.sort()
+
+    return services_state
 
 
 def read_default_target(tree):