Only configure DHCP for real interfaces

Updates the generate-interfaces-file.sh script in
the dhcp-all-interfaces element so that we only
add interfaces that have real MAC addresses.

The generate-interfaces-file.sh script is run early enough
in the boot process (before OVS is initialized) that this
isn't usually a problem unless you execute it manually by hand
after booting. Then you'll end up with network/DHCP
configs for all of your OVS bridges, etc. This
patch avoids configuring all of the virtual interfaces
which have generated MAC addresses.

Change-Id: I7a705084aa5b11305ac0ec5ca37fd2e87a2ae8b7
Closes-bug: 1239479

elements/dhcp-all-interfaces/README.md

@@ -3,8 +3,8 @@ Autodetect network interfaces during boot and configure them for DHCP
 The rationale for this is that we are likely to require multiple
 network interfaces for use cases such as baremetal and there is no way
 to know ahead of time which one is which, so we will simply run a
-DHCP client on all interfaces (except lo) that are visible on the first
-boot.
+DHCP client on all interfaces with real MAC addresses (except lo) that
+are visible on the first boot.
 
 The script /usr/local/sbin/generate-interfaces-file.sh will be called
 early in each boot and will scan available network interfaces and

elements/dhcp-all-interfaces/install.d/generate-interfaces-file.sh

@@ -51,10 +51,14 @@ function disable_interface() {
 }
 
 for interface in $(ls /sys/class/net | grep -v ^lo$) ; do
+  MAC_ADDR_TYPE="$(cat /sys/class/net/${interface}/addr_assign_type)"
+
   echo -n "Inspecting interface: $interface..."
   if ifquery $interface >/dev/null 2>&1 ; then
     echo "Has config, skipping."
-  else
+  elif [ "$MAC_ADDR_TYPE" != "0" ]; then
+    echo "Device has generated MAC, skipping."
+   else
     ip link set dev $interface up >/dev/null 2>&1
     HAS_LINK="$(get_if_link $interface)"