runqemu: Add network bridge support

Qemu supports attaching the virtual machine to an existing network
bridge interface via the qemu-bridge-helper program (as long as the
system is correctly configured to give the user permissions). Add
support for runqemu to do this also via the "bridge=<INTERFACE>"
argument. Note that for this to work correctly, the host
qemu-bridge-helper must be used, not the one that might have been built
by qemu-native. In order for qemu to correctly find this program, a
qemu-oe-bridge-helper program has been added to qemu-helper-native, and
runqemu will use this helper as the bridge helper. The helper will look
for the host qemu-bridge-helper first by looking in the
QEMU_BRIDGE_HELPER environment variable, then by search common paths
where the helper is installed.

(From OE-Core rev: 9e7b38c61c6b84b7f137c733ac5da9414025693d)

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/runqemu

@@ -165,6 +165,7 @@ class BaseConfig(object):
         self.kvm_enabled = False
         self.vhost_enabled = False
         self.slirp_enabled = False
+        self.net_bridge = None
         self.nfs_instance = 0
         self.nfs_running = False
         self.serialconsole = False
@@ -485,6 +486,8 @@ class BaseConfig(object):
                 self.vhost_enabled = True
             elif arg == 'slirp':
                 self.slirp_enabled = True
+            elif arg.startswith('bridge='):
+                self.net_bridge = '%s' % arg[len('bridge='):]
             elif arg == 'snapshot':
                 self.snapshot = True
             elif arg == 'publicvnc':
@@ -802,7 +805,7 @@ class BaseConfig(object):
     def check_and_set(self):
         """Check configs sanity and set when needed"""
         self.validate_paths()
-        if not self.slirp_enabled:
+        if not self.slirp_enabled and not self.net_bridge:
             check_tun()
         # Check audio
         if self.audio_enabled:
@@ -1020,6 +1023,10 @@ class BaseConfig(object):
 
         self.nfs_running = True
 
+    def setup_net_bridge(self):
+        self.set('NETWORK_CMD', '-netdev bridge,br=%s,id=net0,helper=%s -device virtio-net-pci,netdev=net0 ' % (
+            self.net_bridge, os.path.join(self.bindir_native, 'qemu-oe-bridge-helper')))
+
     def setup_slirp(self):
         """Setup user networking"""
 
@@ -1161,7 +1168,9 @@ class BaseConfig(object):
         if sys.stdin.isatty():
             self.saved_stty = subprocess.check_output(("stty", "-g")).decode('utf-8').strip()
         self.network_device = self.get('QB_NETWORK_DEVICE') or self.network_device
-        if self.slirp_enabled:
+        if self.net_bridge:
+            self.setup_net_bridge()
+        elif self.slirp_enabled:
             self.setup_slirp()
         else:
             self.setup_tap()