fix(interfaces): no create, start, stop or delete where libvirt cannot change interfaces

libvirt's udev interface backend (RHEL 9 and later, Debian 12) only reads
interfaces, so the create form and the start, stop and delete buttons
only failed there. The pages ask the host with an invalid definition,
which defines nothing: a backend without define refuses it as not
supported. There they show the interface state and a note instead, and
posts change nothing; the host's devices, needed only by the create
form, are not read. Any other answer keeps the pages as they were.

interfaces/templates/interface.html

@@ -35,6 +35,7 @@
         </div>
     </div>
 
+    {% if changeable is False %}{% include 'interfaces_unchangeable.html' %}{% endif %}
     <div class="row">
         <dl class="ms-3 row">
             <dt class="col-4">{% trans "Interface" %}</dt>
@@ -55,6 +56,9 @@
             <dd class="col-8">{{ start_mode }}</dd>
             <dt class="col-4">{% trans "State" %}</dt>
             <dd class="col-8">
+                {% if changeable is False %}
+                    {% if state == 0 %}{% trans "Inactive" %}{% else %}{% trans "Active" %}{% endif %}
+                {% else %}
                 <form action="" method="post" role="form" aria-label="Interface start/stop/delete form">{% csrf_token %}
                     {% if state == 0 %}
                         <input type="submit" class="btn btn-sm btn-primary" name="start" value="{% trans "Start" %}">
@@ -63,6 +67,7 @@
                         <input type="submit" class="btn btn-sm btn-secondary" name="stop" value="{% trans "Stop" %}" onclick="return confirm('{% trans "Are you sure?" %}')">
                     {% endif %}
                 </form>
+                {% endif %}
             </dd>
         </dl>
 

interfaces/templates/interfaces.html

@@ -8,7 +8,7 @@
 {% block page_heading %}{{ compute.name }} - {% trans "Interfaces" %}{% endblock page_heading %}
 
 {% block page_heading_extra %}
-{% include 'create_iface_block.html' %}
+{% if changeable %}{% include 'create_iface_block.html' %}{% endif %}
 {% endblock page_heading_extra %}
 
 {% block content %}
@@ -42,6 +42,7 @@
         </div>
     </div>
 
+    {% if changeable is False %}{% include 'interfaces_unchangeable.html' %}{% endif %}
     <div class="row">
         {% if not  ifaces_all %}
             <div class="col-lg-12">

interfaces/templates/interfaces_unchangeable.html

@@ -0,0 +1,5 @@
+{% load i18n %}
+{% load bootstrap_icons %}
+<div class="alert alert-info shadow-sm">
+    {% bs_icon 'info-circle' %} {% trans "This host's libvirt does not support changing network interfaces. Configure them directly on the host, for example with NetworkManager." %}
+</div>

interfaces/test_forms.py

@@ -8,7 +8,7 @@ from computes.models import Compute
 from django.contrib.auth import get_user_model
 from django.test import SimpleTestCase, TestCase
 from django.urls import reverse
-from lxml import etree
+from lxml import etree, html
 from vrtManager.interface import wvmInterfaces
 
 from interfaces.forms import AddInterface
@@ -295,6 +295,7 @@ class CreateViewTestCase(TestCase):
             with self.subTest(netdev=netdev), patch("interfaces.views.wvmInterfaces") as conn_cls:
                 conn = conn_cls.return_value
                 conn.get_ifaces.return_value = []
+                conn.can_change_interfaces.return_value = True
                 conn.get_net_devices.return_value = ["eth0", "eth1"]
                 self.client.post(
                     reverse("interfaces", args=[compute.id]),
@@ -309,6 +310,7 @@ class CreateViewTestCase(TestCase):
         with patch("interfaces.views.wvmInterfaces") as conn_cls:
             conn = conn_cls.return_value
             conn.get_ifaces.return_value = []
+            conn.can_change_interfaces.return_value = True
             conn.get_net_devices.side_effect = RuntimeError("nodedev driver not running")
             response = self.client.post(
                 reverse("interfaces", args=[compute.id]),
@@ -320,6 +322,78 @@ class CreateViewTestCase(TestCase):
         self.assertFalse(any("not on this host" in m for m in messages), messages)
 
 
+class UnchangeableHostTestCase(TestCase):
+    """A host whose libvirt cannot change interfaces (udev backend) gets no
+    create form and no start/stop/delete, only a note; posts change nothing."""
+
+    NOTE = "does not support changing network interfaces"
+
+    def setUp(self):
+        self.client.force_login(get_user_model().objects.create_superuser("iface_ro", "ro@example.com", "x"))
+        self.compute = Compute.objects.create(name="iface-ro", hostname="127.0.0.1:1", login="root", password="", type=1)
+
+    def interfaces_page(self, changeable, post=None):
+        with patch("interfaces.views.wvmInterfaces") as conn_cls:
+            conn = conn_cls.return_value
+            conn.get_ifaces.return_value = []
+            conn.can_change_interfaces.return_value = changeable
+            conn.get_net_devices.return_value = ["eth0", "eth1"]
+            url = reverse("interfaces", args=[self.compute.id])
+            response = self.client.post(url, post) if post else self.client.get(url)
+        return conn, response.content.decode()
+
+    def test_the_interfaces_page_offers_create_only_where_it_works(self):
+        for changeable in (True, False):
+            with self.subTest(changeable=changeable):
+                conn, page = self.interfaces_page(changeable)
+                self.assertEqual("#AddInterface" in page, changeable)
+                self.assertEqual(self.NOTE in page, not changeable)
+                # the devices are only the form's choices
+                self.assertEqual(conn.get_net_devices.called, changeable)
+
+    def test_a_create_post_creates_nothing(self):
+        conn, page = self.interfaces_page(False, {**BASE, "netdev": "eth1", "ipv6_type": "none", "create": ""})
+        conn.create_iface.assert_not_called()
+        self.assertIn(self.NOTE, page)
+
+    def interface_page(self, changeable, state, post=None):
+        with patch("interfaces.views.wvmInterface") as conn_cls:
+            conn = conn_cls.return_value
+            conn.can_change_interfaces.return_value = changeable
+            conn.is_active.return_value = state
+            conn.get_bridge_slave_ifaces.return_value = []
+            url = reverse("interface", args=[self.compute.id, "br0"])
+            response = self.client.post(url, post) if post else self.client.get(url)
+        return conn, response
+
+    def test_the_interface_page_shows_the_state_without_actions(self):
+        for state, shown in ((1, "Active"), (0, "Inactive")):
+            with self.subTest(state=state):
+                _conn, response = self.interface_page(False, state)
+                page = response.content.decode()
+                self.assertNotIn('name="start"', page)
+                self.assertNotIn('name="stop"', page)
+                state_cell = html.fromstring(page).xpath("//dt[normalize-space()='State']/following-sibling::dd[1]")[0]
+                self.assertEqual(state_cell.text_content().strip(), shown)
+                self.assertIn(self.NOTE, page)
+        _conn, response = self.interface_page(True, 0)
+        self.assertIn('name="start"', response.content.decode())
+
+    def test_a_host_that_could_not_be_read_keeps_the_page_as_it_was(self):
+        with patch("interfaces.views.wvmInterface", side_effect=libvirt.libvirtError("unreachable")):
+            page = self.client.get(reverse("interface", args=[self.compute.id, "br0"])).content.decode()
+        self.assertNotIn(self.NOTE, page)
+        self.assertIn("Interface start/stop/delete form", page)
+
+    def test_start_stop_and_delete_posts_change_nothing(self):
+        for action in ("start", "stop", "delete"):
+            with self.subTest(action=action):
+                conn, response = self.interface_page(False, 1, {action: ""})
+                self.assertEqual(response.status_code, 200)
+                for method in (conn.start_iface, conn.stop_iface, conn.delete_iface):
+                    method.assert_not_called()
+
+
 class EthernetDeviceTestCase(SimpleTestCase):
     def test_an_ethernet_interface_needs_no_bridge_member(self):
         self.assertTrue(form(itype="ethernet", name="eth0", netdev="", ipv6_type="none").is_valid())

interfaces/test_live_interfaces.py

@@ -0,0 +1,42 @@
+"""Live check that asking a host whether it can change interfaces defines
+nothing, and that the interfaces page follows the answer. Runs only with
+TEST_LIBVIRT_HOST set; TEST_LIBVIRT_SSH_HOST/_LOGIN add an ssh compute."""
+
+import os
+import unittest
+
+from computes.models import Compute
+from django.contrib.auth import get_user_model
+from django.test import TestCase
+from django.urls import reverse
+from vrtManager.connection import wvmConnect
+
+
+@unittest.skipUnless(os.environ.get("TEST_LIBVIRT_HOST"), "Set TEST_LIBVIRT_HOST to run the live libvirt tests")
+class LiveInterfacesTestCase(TestCase):
+    def hosts(self):
+        yield "tcp", (
+            os.environ["TEST_LIBVIRT_HOST"],
+            os.environ.get("TEST_LIBVIRT_LOGIN", ""),
+            os.environ.get("TEST_LIBVIRT_PASSWORD", ""),
+            int(os.environ.get("TEST_LIBVIRT_TYPE", 1)),
+        )
+        if os.environ.get("TEST_LIBVIRT_SSH_HOST"):
+            yield "ssh", (os.environ["TEST_LIBVIRT_SSH_HOST"], os.environ.get("TEST_LIBVIRT_SSH_LOGIN", "root"), "", 2)
+
+    def test_the_question_defines_nothing_and_the_page_follows_the_answer(self):
+        self.client.force_login(get_user_model().objects.create_superuser("live-iface", "li@example.com", "x"))
+        for name, args in self.hosts():
+            with self.subTest(name):
+                conn = wvmConnect(*args)
+                before = sorted(i.XMLDesc(0) for i in conn.wvm.listAllInterfaces(0))
+                changeable = conn.can_change_interfaces()
+                self.assertIsInstance(changeable, bool)
+                self.assertEqual(sorted(i.XMLDesc(0) for i in conn.wvm.listAllInterfaces(0)), before)
+                hostname, login, password, conn_type = args
+                compute = Compute.objects.create(
+                    name=f"live-{name}", hostname=hostname, login=login, password=password, type=conn_type
+                )
+                page = self.client.get(reverse("interfaces", args=[compute.id])).content.decode()
+                self.assertEqual("#AddInterface" in page, changeable)
+                self.assertEqual("does not support changing network interfaces" in page, not changeable)

interfaces/views.py

@@ -29,13 +29,16 @@ def interfaces(request, compute_id):
             compute.type
         )
         ifaces = conn.get_ifaces()
+        changeable = conn.can_change_interfaces()
 
+        # the host's devices are only the create form's choices
         netdevs, netdev_error = [], None
-        try:
-            netdevs = conn.get_net_devices()
-        except Exception as err:
-            netdev_error = err
-            messages.error(request, _("The network devices of this host could not be read: %(error)s") % {"error": err})
+        if changeable:
+            try:
+                netdevs = conn.get_net_devices()
+            except Exception as err:
+                netdev_error = err
+                messages.error(request, _("The network devices of this host could not be read: %(error)s") % {"error": err})
 
         for iface in ifaces:
             interf = wvmInterface(
@@ -48,8 +51,9 @@ def interfaces(request, compute_id):
             ifaces_all.append(interf.get_details())
 
         if request.method == "POST":
-            # without the host's devices nothing can be checked, so nothing is created
-            if "create" in request.POST and netdev_error is None:
+            # the page says why nothing is created on a host that cannot change
+            # interfaces; without the host's devices nothing can be checked
+            if "create" in request.POST and changeable and netdev_error is None:
                 form = AddInterface(request.POST, netdevs=netdevs)
                 if form.is_valid():
                     data = form.cleaned_data
@@ -108,8 +112,10 @@ def interface(request, compute_id, iface):
         ipv6_type = conn.get_ipv6_type()
         bridge = conn.get_bridge()
         slave_ifaces = conn.get_bridge_slave_ifaces()
+        changeable = conn.can_change_interfaces()
 
-        if request.method == "POST":
+        # the page says why nothing is done on a host that cannot change interfaces
+        if request.method == "POST" and changeable:
             if "stop" in request.POST:
                 conn.stop_iface()
                 return HttpResponseRedirect(request.get_full_path())