net_util: Add helper for generating a random local MAC

We must ensure our MAC addresses do not conflict with a global one.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

Cargo.lock

@@ -157,6 +157,7 @@ version = "0.1.0"
 dependencies = [
  "libc 0.2.54 (registry+https://github.com/rust-lang/crates.io-index)",
  "net_gen 0.1.0",
+ "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.91 (registry+https://github.com/rust-lang/crates.io-index)",
  "vmm-sys-util 0.1.0 (git+https://github.com/liujing2/vmm-sys-util)",
 ]

net_util/Cargo.toml

@@ -5,6 +5,7 @@ authors = ["The Chromium OS Authors"]
 
 [dependencies]
 libc = ">=0.2.39"
+rand = ">=0.6.5"
 serde = ">=1.0.27"
 
 net_gen = { path = "../net_gen" }

net_util/src/lib.rs

@@ -11,6 +11,7 @@
 #[macro_use]
 extern crate lazy_static;
 extern crate libc;
+extern crate rand;
 extern crate serde;
 
 extern crate net_gen;

net_util/src/mac.rs

@@ -5,6 +5,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the THIRD-PARTY file.
 
+use rand::Rng;
 use std::result::Result;
 
 use serde::de::{Deserialize, Deserializer, Error};
@@ -72,6 +73,18 @@ impl MacAddr {
             b[0], b[1], b[2], b[3], b[4], b[5]
         )
     }
+
+    pub fn local_random() -> MacAddr {
+        // Generate a fully random MAC
+        let mut random_bytes = rand::thread_rng().gen::<[u8; MAC_ADDR_LEN]>();
+
+        // Set the first byte to make the OUI a locally administered OUI
+        random_bytes[0] = 0x2e;
+
+        MacAddr {
+            bytes: random_bytes,
+        }
+    }
 }
 
 impl Serialize for MacAddr {