interface: Improve udev backend device type id

Refactored the interface device type identification to make it more
clear about the operations. Add support for udev devtype to detect
VLANs on Linux 3.7 and newer. Move VLAN detection based on device
name to fallback case.

src/interface/interface_backend_udev.c

@@ -684,9 +684,6 @@ udevIfaceGetIfaceDefVlan(struct udev *udev ATTRIBUTE_UNUSED,
     vid[0] = '\0';
     vid++;
 
-    /* Set our type to VLAN  */
-    ifacedef->type = VIR_INTERFACE_TYPE_VLAN;
-
     /* Set the VLAN specifics */
     ifacedef->data.vlan.tag = vid;
     ifacedef->data.vlan.devname = vlan_parent_dev;
@@ -707,6 +704,7 @@ udevIfaceGetIfaceDef(struct udev *udev, const char *name)
     unsigned int mtu;
     const char *mtu_str;
     char *vlan_parent_dev = NULL;
+    const char *devtype;
 
     /* Allocate our interface definition structure */
     if (VIR_ALLOC(ifacedef) < 0) {
@@ -716,7 +714,6 @@ udevIfaceGetIfaceDef(struct udev *udev, const char *name)
 
     /* Clear our structure and set safe defaults */
     ifacedef->startmode = VIR_INTERFACE_START_UNSPECIFIED;
-    ifacedef->type = VIR_INTERFACE_TYPE_ETHERNET;
     ifacedef->name = strdup(name);
 
     if (!ifacedef->name) {
@@ -753,18 +750,43 @@ udevIfaceGetIfaceDef(struct udev *udev, const char *name)
     ifacedef->nprotos = 0;
     ifacedef->protos = NULL;
 
-    /* Check if its a VLAN since we can have a VLAN of any of the
-     * other devices */
-    vlan_parent_dev = strrchr(name, '.');
-    if (vlan_parent_dev) {
+    /* Check the type of device we are working with based on the devtype */
+    devtype = udev_device_get_devtype(dev);
+
+    /* Set our type to ethernet as the default case */
+    ifacedef->type = VIR_INTERFACE_TYPE_ETHERNET;
+
+    if (STREQ_NULLABLE(devtype, "vlan")) {
+        /* This only works on modern kernels (3.7 and newer)
+         * e949b09b71d975a82f13ac88ce4ad338fed213da
+         */
+        ifacedef->type = VIR_INTERFACE_TYPE_VLAN;
+    } else if (STREQ_NULLABLE(devtype, "bridge")) {
+        ifacedef->type = VIR_INTERFACE_TYPE_BRIDGE;
+    }
+
+    /* Fallback checks if the devtype check didn't work. */
+    if (ifacedef->type == VIR_INTERFACE_TYPE_ETHERNET) {
+        /* First check if its a VLAN based on the name containing a dot,
+         * to prevent false positives
+         */
+        vlan_parent_dev = strrchr(name, '.');
+        if (vlan_parent_dev) {
+            ifacedef->type = VIR_INTERFACE_TYPE_VLAN;
+        }
+    }
+
+    switch (ifacedef->type) {
+    case VIR_INTERFACE_TYPE_VLAN:
         if (udevIfaceGetIfaceDefVlan(udev, dev, name, ifacedef))
             goto cleanup;
-    } else if (STREQ_NULLABLE(udev_device_get_devtype(dev), "bridge")) {
+        break;
+    case VIR_INTERFACE_TYPE_BRIDGE:
         if (udevIfaceGetIfaceDefBridge(udev, dev, name, ifacedef) < 0)
             goto cleanup;
-    } else {
-        /* Set our type to ethernet */
-        ifacedef->type = VIR_INTERFACE_TYPE_ETHERNET;
+        break;
+    case VIR_INTERFACE_TYPE_ETHERNET:
+        break;
     }
 
     udev_device_unref(dev);