Make modprobe module check for builtins as well (#37150)

Without this modprobe always reports changed when modprobe-ing a builtin module.

With this, if a kernel module is a builtin, the modprobe module will:
- succeed (without incorrectly reporting changed) if ``state`` is ``present``;
- fail if ``state`` is ``absent``

The failure will have whatever error message modprobe returns when
attempting to remove a builtin module. For example:
``modprobe: ERROR: Module nfs is builtin.``

changelogs/fragments/37150-make_modprobe_module_check_for_builtins_as_well.yaml

@@ -0,0 +1,3 @@
+---
+bugfixes:
+- "modprobe - The modprobe module now detects builtin kernel modules. If a kernel module is builtin the modprobe module will now: succeed (without incorrectly reporting changed) if ``state`` is ``present``; and fail if ``state`` is ``absent`` (with an error message like ``modprobe: ERROR: Module nfs is builtin.``). (https://github.com/ansible/ansible/pull/37150)"

docs/docsite/rst/porting_guides/porting_guide_2.8.rst

@@ -131,6 +131,13 @@ Noteworthy module changes
 * The ``na_ontap_cluster_peer`` module has replaced ``source_intercluster_lif`` and ``dest_intercluster_lif`` string options with
   ``source_intercluster_lifs`` and ``dest_intercluster_lifs`` list options
 
+* The ``modprobe`` module now detects kernel builtins. Previously, attempting to remove (with ``state: absent``)
+  a builtin kernel module succeeded without any error message because ``modprobe`` did not detect the module as
+  ``present``. Now, ``modprobe`` will fail if a kernel module is builtin and ``state: absent`` (with an error message
+  from the modprobe binary like ``modprobe: ERROR: Module nfs is builtin.``), and it will succeed without reporting
+  changed if ``state: present``. Any playbooks that are using ``changed_when: no`` to mask this quirk can safely
+  remove that workaround. To get the previous behavior when applying ``state: absent`` to a builtin kernel module,
+  use ``failed_when: false`` or ``ignore_errors: true`` in your playbook.
 
 Plugins
 =======

lib/ansible/modules/system/modprobe.py

@@ -83,14 +83,22 @@ def main():
 
     # Check if module is present
     try:
-        modules = open('/proc/modules')
         present = False
+        with open('/proc/modules') as modules:
             module_name = name.replace('-', '_') + ' '
             for line in modules:
                 if line.startswith(module_name):
                     present = True
                     break
-        modules.close()
+        if not present:
+            command = [module.get_bin_path('uname', True), '-r']
+            rc, uname_kernel_release, err = module.run_command(command)
+            module_file = '/' + name + '.ko'
+            with open('/lib/modules/' + uname_kernel_release + '/modules.builtin') as builtins:
+                for line in builtins:
+                    if line.endswith(module_file):
+                        present = True
+                        break
     except IOError as e:
         module.fail_json(msg=to_native(e), exception=traceback.format_exc(), **result)