Make cpufrequtils optional (#90)

cpufrequtils is not available on some architectures,
such as ppc64el.
In these cases, previously the charm would fail to install,
crashing on trying to install cpufrequtils.

So now the charm will install cpufrequtils if it is available
and continue as usual.
If cpufrequtils is not available however,
the charm will skip attempting to install cpufrequtils,
and ignore the governor config option.

Also some tox.ini improvements:
- remove the envdir option from tox.ini;
  this is not a recommended way to share environments.
- switch to flake8-pyproject
  - appears more maintained
  - lets us use the original flake8 command

src/config.yaml

@@ -163,6 +163,9 @@ options:
                         Recommended option when Bios control power is set to the OS.
         - 'performance'
         - 'powersave'
+
+        On some architectures, cpufrequtils is not available.
+        In these cases, this config option will be ignored.
   resolved-cache-mode:
     type: string
     default: ""

src/layer.yaml

@@ -25,7 +25,4 @@ options:
         include_system_packages: true
         packages:
             - python3-yaml
-    apt:
-        packages:
-            - cpufrequtils
 repo: https://github.com/canonical/charm-sysconfig

src/lib/lib_sysconfig.py

@@ -659,6 +659,21 @@ def install_configured_kernel(self):
         apt_install("linux-image-{}".format(configured))
         self.boot_resources.set_resource(KERNEL)
 
+    def install_cpufrequtils(self):
+        """Install cpufrequtils if available.
+
+        Return True if cpufrequtils is available
+        and installation was successful.
+        """
+        apt_update()
+        if subprocess.check_output(
+            ["apt-cache", "search", "--names-only", "^cpufrequtils$"]
+        ).strip():
+            apt_install("cpufrequtils", fatal=True)
+            return True
+        else:
+            return False
+
     def update_cpufreq(self):
         """Update /etc/default/cpufrequtils and restart cpufrequtils service."""
         if self.governor not in ("", "performance", "powersave"):

src/reactive/sysconfig.py

@@ -58,8 +58,19 @@ def install_sysconfig():
         hookenv.status_set("blocked", "configuration parameters not valid.")
         return
 
+    if syshelper.install_cpufrequtils():
+        set_flag("sysconfig.cpufrequtils-installed")
+    else:
+        hookenv.log(
+            "cpufrequtils package not found: governor config option will be ignored.",
+            hookenv.WARNING,
+        )
+
     syshelper.install_configured_kernel()
-    syshelper.update_cpufreq()
+
+    if is_flag_set("sysconfig.cpufrequtils-installed"):
+        syshelper.update_cpufreq()
+
     syshelper.update_grub_file()
     syshelper.update_systemd_system_file()
     syshelper.update_systemd_resolved()
@@ -86,8 +97,9 @@ def config_changed():
         syshelper.install_configured_kernel()
 
     # cpufreq
-    if syshelper.charm_config.changed("governor") or helpers.any_file_changed(
-        [CPUFREQUTILS]
+    if is_flag_set("sysconfig.cpufrequtils-installed") and (
+        syshelper.charm_config.changed("governor")
+        or helpers.any_file_changed([CPUFREQUTILS])
     ):
         syshelper.update_cpufreq()
 
@@ -215,7 +227,10 @@ def remove_configuration():
     """
     hookenv.status_set("maintenance", "removing sysconfig configurations")
     syshelper = SysConfigHelper()
-    syshelper.remove_cpufreq_configuration()
+
+    if is_flag_set("sysconfig.cpufrequtils-installed"):
+        syshelper.remove_cpufreq_configuration()
+
     syshelper.remove_grub_configuration()
     syshelper.remove_systemd_configuration()
     syshelper.remove_resolved_configuration()

src/tests/unit/test_lib.py

@@ -1062,7 +1062,7 @@ def test_update_sysctl(self, check_call, config):
 
         mock_file.assert_called_with(lib_sysconfig.SYSCTL_CONF, "w")
         handle = mock_file()
-        handle.write.has_calls(
+        handle.write.assert_has_calls(
             [mock.call("net.ipv4.ip_forward=1\n"), mock.call("vm.swappiness=60\n")]
         )
         check_call.assert_called_with(["sysctl", "-p", lib_sysconfig.SYSCTL_CONF])
@@ -1101,3 +1101,39 @@ def test_remove_irqbalance_configuration(self, render, log, config, restart):
         )
 
         restart.assert_called()
+
+    @mock.patch("lib_sysconfig.apt_install")
+    @mock.patch("lib_sysconfig.apt_update")
+    @mock.patch("lib_sysconfig.subprocess")
+    @mock.patch("lib_sysconfig.hookenv.config")
+    def test_install_cpufrequtils_success(
+        self, _mock_config, mock_subprocess, mock_apt_update, mock_apt_install
+    ):
+        """Verify it does install cpufrequtils when it's available."""
+        mock_subprocess.check_output.return_value = (
+            "cpufrequtils - utilities to deal with the cpufreq Linux kernel feature"
+        )
+        sysh = lib_sysconfig.SysConfigHelper()
+
+        result = sysh.install_cpufrequtils()
+
+        assert result is True
+        mock_apt_update.assert_called_once_with()
+        mock_apt_install.assert_called_once_with("cpufrequtils", fatal=True)
+
+    @mock.patch("lib_sysconfig.apt_install")
+    @mock.patch("lib_sysconfig.apt_update")
+    @mock.patch("lib_sysconfig.subprocess")
+    @mock.patch("lib_sysconfig.hookenv.config")
+    def test_install_cpufrequtils_not_found(
+        self, _mock_config, mock_subprocess, mock_apt_update, mock_apt_install
+    ):
+        """Verify it doesn't install cpufrequtils when it's not available."""
+        mock_subprocess.check_output.return_value = ""
+        sysh = lib_sysconfig.SysConfigHelper()
+
+        result = sysh.install_cpufrequtils()
+
+        assert result is False
+        mock_apt_update.assert_called_once_with()
+        mock_apt_install.assert_not_called()

tox.ini

@@ -31,21 +31,20 @@ passenv =
 
 [testenv:lint]
 commands =
-    pflake8
+    flake8
     black --check --diff --color .
     isort --check --diff --color .
 deps =
     black<24.0.0 # TODO: Remove pin once we make our linter pass on it
     flake8
-    pyproject-flake8
+    flake8-pyproject
     flake8-docstrings
     pep8-naming
     flake8-colors
     colorama
     isort
 
 [testenv:reformat]
-envdir = {toxworkdir}/lint
 commands =
     black .
     isort .