network: Added GetBridgePorts() and tests

network/utils.go

@@ -225,3 +225,32 @@ func ParseInterfaceType(sysPath, interfaceName string) InterfaceType {
 
 	return UnknownInterface
 }
+
+// GetBridgePorts extracts and returns the names of all interfaces configured as
+// ports of the given bridgeName from the Linux kernel userspace SYSFS location
+// "<sysPath/<bridgeName>/brif/*". SysClassNetPath should be passed as sysPath.
+// Returns an empty result if the ports cannot be determined reliably for any
+// reason, or if there are no configured ports for the bridge.
+//
+// Example call: network.GetBridgePorts(network.SysClassNetPath, "br-eth1")
+func GetBridgePorts(sysPath, bridgeName string) []string {
+	portsGlobPath := filepath.Join(sysPath, bridgeName, "brif", "*")
+	// Glob ignores I/O errors and can only return ErrBadPattern, which we treat
+	// as no results, but for debugging we're still logging the error.
+	paths, err := filepath.Glob(portsGlobPath)
+	if err != nil {
+		logger.Debugf("ignoring error traversing path %q: %v", portsGlobPath, err)
+	}
+
+	if len(paths) == 0 {
+		return nil
+	}
+
+	// We need to convert full paths like /sys/class/net/br-eth0/brif/eth0 to
+	// just names.
+	names := make([]string, len(paths))
+	for i := range paths {
+		names[i] = filepath.Base(paths[i])
+	}
+	return names
+}

network/utils_test.go

@@ -189,6 +189,39 @@ func (*UtilsSuite) TestParseInterfaceType(c *gc.C) {
 	c.Check(result, gc.Equals, network.UnknownInterface)
 }
 
+func (*UtilsSuite) TestGetBridgePorts(c *gc.C) {
+	fakeSysPath := filepath.Join(c.MkDir(), network.SysClassNetPath)
+	err := os.MkdirAll(fakeSysPath, 0700)
+	c.Check(err, jc.ErrorIsNil)
+
+	writeFakePorts := func(bridgeName string, portNames ...string) {
+		fakePortsPath := filepath.Join(fakeSysPath, bridgeName, "brif")
+		err := os.MkdirAll(fakePortsPath, 0700)
+		c.Check(err, jc.ErrorIsNil)
+
+		for _, portName := range portNames {
+			portPath := filepath.Join(fakePortsPath, portName)
+			err = ioutil.WriteFile(portPath, []byte(""), 0644)
+			c.Check(err, jc.ErrorIsNil)
+		}
+	}
+
+	result := network.GetBridgePorts(fakeSysPath, "missing")
+	c.Check(result, gc.IsNil)
+
+	writeFakePorts("br-eth0")
+	result = network.GetBridgePorts(fakeSysPath, "br-eth0")
+	c.Check(result, gc.IsNil)
+
+	writeFakePorts("br-eth0", "eth0")
+	result = network.GetBridgePorts(fakeSysPath, "br-eth0")
+	c.Check(result, jc.DeepEquals, []string{"eth0"})
+
+	writeFakePorts("br-ovs", "eth0", "eth1", "eth2")
+	result = network.GetBridgePorts(fakeSysPath, "br-ovs")
+	c.Check(result, jc.DeepEquals, []string{"eth0", "eth1", "eth2"})
+}
+
 type mockListener struct {
 	net.Listener
 }