filter: allow enabling/disabling rules via envvars

E.g. forcing a MBIM modem to run in AT-only mode:

  # MM_FILTER_RULE_NET=0     \
    MM_FILTER_RULE_CDC_WDM=0 \
    /usr/sbin/ModemManager --debug

This is just for quick testing for now.

src/mm-base-manager.c

@@ -1127,13 +1127,7 @@ initable_init (GInitable *initable,
 #endif
 
     /* Create filter */
-    priv->filter = mm_filter_new (MM_FILTER_RULE_VIRTUAL              |
+    priv->filter = mm_filter_new (MM_FILTER_RULE_ALL);
-                                  MM_FILTER_RULE_NET                  |
-                                  MM_FILTER_RULE_CDC_WDM              |
-                                  MM_FILTER_RULE_TTY                  |
-                                  MM_FILTER_RULE_TTY_BLACKLIST        |
-                                  MM_FILTER_RULE_TTY_MANUAL_SCAN_ONLY |
-                                  MM_FILTER_RULE_TTY_PLATFORM_DRIVER);
 
     /* Create plugin manager */
     priv->plugin_manager = mm_plugin_manager_new (priv->plugin_dir, error);

src/mm-filter.c

@@ -105,6 +105,43 @@ mm_filter_port (MMFilter        *self,
     return FALSE;
 }
 
+/*****************************************************************************/
+/* Use filter rule names as environment variables to control them on startup:
+ *  - MM_FILTER_RULE_XXX=1 to explicitly enable the rule.
+ *  - MM_FILTER_RULE_XXX=0 to explicitly disable the rule.
+ */
+
+static MMFilterRule
+filter_rule_env_process (MMFilterRule enabled_rules)
+{
+    MMFilterRule  updated_rules = enabled_rules;
+    GFlagsClass  *flags_class;
+    guint         i;
+
+    flags_class = g_type_class_ref (MM_TYPE_FILTER_RULE);
+
+    for (i = 0; (1 << i) & MM_FILTER_RULE_ALL; i++) {
+        GFlagsValue *flags_value;
+        const gchar *env_value;
+
+        flags_value = g_flags_get_first_value (flags_class, (1 << i));
+        g_assert (flags_value);
+
+        env_value = g_getenv (flags_value->value_name);
+        if (!env_value)
+            continue;
+
+        if (g_str_equal (env_value, "0"))
+            updated_rules &= ~(1 << i);
+        else if (g_str_equal (env_value, "1"))
+            updated_rules |= (1 << i);
+    }
+
+    g_type_class_unref (flags_class);
+
+    return updated_rules;
+}
+
 /*****************************************************************************/
 
 MMFilter *
@@ -113,7 +150,7 @@ mm_filter_new (MMFilterRule enabled_rules)
     MMFilter *self;
 
     self = g_object_new (MM_TYPE_FILTER,
-                         MM_FILTER_ENABLED_RULES, enabled_rules,
+                         MM_FILTER_ENABLED_RULES, filter_rule_env_process (enabled_rules),
                          NULL);
 
 #define RULE_ENABLED_STR(flag) ((self->priv->enabled_rules & flag) ? "yes" : "no")

src/mm-filter.h

@@ -54,6 +54,15 @@ typedef enum { /*< underscore_name=mm_filter_rule >*/
     MM_FILTER_RULE_TTY_PLATFORM_DRIVER  = 1 << 6,
 } MMFilterRule;
 
+#define MM_FILTER_RULE_ALL                 \
+    (MM_FILTER_RULE_VIRTUAL              | \
+     MM_FILTER_RULE_NET                  | \
+     MM_FILTER_RULE_CDC_WDM              | \
+     MM_FILTER_RULE_TTY                  | \
+     MM_FILTER_RULE_TTY_BLACKLIST        | \
+     MM_FILTER_RULE_TTY_MANUAL_SCAN_ONLY | \
+     MM_FILTER_RULE_TTY_PLATFORM_DRIVER)
+
 MMFilter *mm_filter_new (MMFilterRule enabled_rules);
 
 gboolean mm_filter_port (MMFilter        *self,