vmm, vm-virtio: Stop always autogenerating a host MAC address

This removes the need to use CAP_NET_ADMIN privileges and instead the
host MAC addres is either provided by the user or alternatively it is
retrieved from the kernel.

TEST=Run cloud-hypervisor without CAP_NET_ADMIN permission and a
preconfigured tap device:

sudo ip tuntap add name tap0 mode tap
sudo ifconfig tap0 192.168.249.1 netmask 255.255.255.0 up
cargo clean
cargo build
target/debug/cloud-hypervisor --serial tty --console off --kernel ~/src/rust-hypervisor-firmware/target/target/release/hypervisor-fw --disk path=~/workloads/clear-33190-kvm.img --net tap=tap0

VM was also rebooted to check that works correctly.

Fixes: #1274

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vhost_user_net/src/lib.rs

@@ -141,7 +141,7 @@ impl VhostUserNetBackend {
             ifname,
             Some(ip_addr),
             Some(netmask),
-            Some(host_mac),
+            &mut Some(host_mac),
             num_queues / 2,
         )
         .map_err(Error::OpenTap)?;

vm-virtio/src/net.rs

@@ -465,7 +465,7 @@ impl Net {
         ip_addr: Option<Ipv4Addr>,
         netmask: Option<Ipv4Addr>,
         guest_mac: Option<MacAddr>,
-        host_mac: Option<MacAddr>,
+        host_mac: &mut Option<MacAddr>,
         iommu: bool,
         num_queues: usize,
         queue_size: u16,

vm-virtio/src/net_util.rs

@@ -122,6 +122,8 @@ pub enum Error {
     TapSetNetmask(TapError),
     /// Setting MAC address failed
     TapSetMac(TapError),
+    /// Getting MAC address failed
+    TapGetMac(TapError),
     /// Setting tap interface offload flags failed.
     TapSetOffload(TapError),
     /// Setting vnet header size failed.
@@ -539,7 +541,7 @@ pub fn open_tap(
     if_name: Option<&str>,
     ip_addr: Option<Ipv4Addr>,
     netmask: Option<Ipv4Addr>,
-    host_mac: Option<MacAddr>,
+    host_mac: &mut Option<MacAddr>,
     num_rx_q: usize,
 ) -> Result<Vec<Tap>> {
     let mut taps: Vec<Tap> = Vec::new();
@@ -568,7 +570,9 @@ pub fn open_tap(
                 tap.set_netmask(mask).map_err(Error::TapSetNetmask)?;
             }
             if let Some(mac) = host_mac {
-                tap.set_mac_addr(mac).map_err(Error::TapSetMac)?
+                tap.set_mac_addr(*mac).map_err(Error::TapSetMac)?
+            } else {
+                *host_mac = Some(tap.get_mac_addr().map_err(Error::TapGetMac)?)
             }
             tap.enable().map_err(Error::TapEnable)?;
             tap.set_offload(flag).map_err(Error::TapSetOffload)?;

vmm/src/config.rs

@@ -683,8 +683,8 @@ pub struct NetConfig {
     pub mask: Ipv4Addr,
     #[serde(default = "default_netconfig_mac")]
     pub mac: MacAddr,
-    #[serde(default = "default_netconfig_mac")]
-    pub host_mac: MacAddr,
+    #[serde(default)]
+    pub host_mac: Option<MacAddr>,
     #[serde(default)]
     pub iommu: bool,
     #[serde(default = "default_netconfig_num_queues")]
@@ -729,7 +729,7 @@ impl Default for NetConfig {
             ip: default_netconfig_ip(),
             mask: default_netconfig_mask(),
             mac: default_netconfig_mac(),
-            host_mac: default_netconfig_mac(),
+            host_mac: None,
             iommu: false,
             num_queues: default_netconfig_num_queues(),
             queue_size: default_netconfig_queue_size(),
@@ -776,10 +776,7 @@ impl NetConfig {
             .convert("mac")
             .map_err(Error::ParseNetwork)?
             .unwrap_or_else(default_netconfig_mac);
-        let host_mac = parser
-            .convert("host_mac")
-            .map_err(Error::ParseNetwork)?
-            .unwrap_or_else(default_netconfig_mac);
+        let host_mac = parser.convert("host_mac").map_err(Error::ParseNetwork)?;
         let iommu = parser
             .convert::<Toggle>("iommu")
             .map_err(Error::ParseNetwork)?
@@ -1633,7 +1630,7 @@ mod tests {
             NetConfig::parse("mac=de:ad:be:ef:12:34,host_mac=12:34:de:ad:be:ef")?,
             NetConfig {
                 mac: MacAddr::parse_str("de:ad:be:ef:12:34").unwrap(),
-                host_mac: MacAddr::parse_str("12:34:de:ad:be:ef").unwrap(),
+                host_mac: Some(MacAddr::parse_str("12:34:de:ad:be:ef").unwrap()),
                 ..Default::default()
             }
         );
@@ -1642,7 +1639,7 @@ mod tests {
             NetConfig::parse("mac=de:ad:be:ef:12:34,host_mac=12:34:de:ad:be:ef,id=mynet0")?,
             NetConfig {
                 mac: MacAddr::parse_str("de:ad:be:ef:12:34").unwrap(),
-                host_mac: MacAddr::parse_str("12:34:de:ad:be:ef").unwrap(),
+                host_mac: Some(MacAddr::parse_str("12:34:de:ad:be:ef").unwrap()),
                 id: Some("mynet0".to_owned()),
                 ..Default::default()
             }
@@ -1654,7 +1651,7 @@ mod tests {
             )?,
             NetConfig {
                 mac: MacAddr::parse_str("de:ad:be:ef:12:34").unwrap(),
-                host_mac: MacAddr::parse_str("12:34:de:ad:be:ef").unwrap(),
+                host_mac: Some(MacAddr::parse_str("12:34:de:ad:be:ef").unwrap()),
                 tap: Some("tap0".to_owned()),
                 ip: "192.168.100.1".parse().unwrap(),
                 mask: "255.255.255.128".parse().unwrap(),
@@ -1668,7 +1665,7 @@ mod tests {
             )?,
             NetConfig {
                 mac: MacAddr::parse_str("de:ad:be:ef:12:34").unwrap(),
-                host_mac: MacAddr::parse_str("12:34:de:ad:be:ef").unwrap(),
+                host_mac: Some(MacAddr::parse_str("12:34:de:ad:be:ef").unwrap()),
                 vhost_user: true,
                 vhost_socket: Some("/tmp/sock".to_owned()),
                 ..Default::default()
@@ -1679,7 +1676,7 @@ mod tests {
             NetConfig::parse("mac=de:ad:be:ef:12:34,host_mac=12:34:de:ad:be:ef,num_queues=4,queue_size=1024,iommu=on")?,
             NetConfig {
                 mac: MacAddr::parse_str("de:ad:be:ef:12:34").unwrap(),
-                host_mac: MacAddr::parse_str("12:34:de:ad:be:ef").unwrap(),
+                host_mac: Some(MacAddr::parse_str("12:34:de:ad:be:ef").unwrap()),
                 num_queues: 4,
                 queue_size: 1024,
                 iommu: true,

vmm/src/device_manager.rs

@@ -1512,13 +1512,17 @@ impl DeviceManager {
             .args(&[
                 "--net-backend",
                 &format!(
-                    "ip={},mask={},socket={},num_queues={},queue_size={},host_mac={}",
+                    "ip={},mask={},socket={},num_queues={},queue_size={}{}",
                     net_cfg.ip,
                     net_cfg.mask,
                     &socket,
                     net_cfg.num_queues,
                     net_cfg.queue_size,
-                    net_cfg.host_mac
+                    if let Some(mac) = net_cfg.host_mac {
+                        format!(",host_mac={:}", mac)
+                    } else {
+                        "".to_owned()
+                    }
                 ),
             ])
             .spawn()
@@ -1583,7 +1587,7 @@ impl DeviceManager {
                         None,
                         None,
                         Some(net_cfg.mac),
-                        Some(net_cfg.host_mac),
+                        &mut net_cfg.host_mac,
                         net_cfg.iommu,
                         net_cfg.num_queues,
                         net_cfg.queue_size,
@@ -1598,7 +1602,7 @@ impl DeviceManager {
                         Some(net_cfg.ip),
                         Some(net_cfg.mask),
                         Some(net_cfg.mac),
-                        Some(net_cfg.host_mac),
+                        &mut net_cfg.host_mac,
                         net_cfg.iommu,
                         net_cfg.num_queues,
                         net_cfg.queue_size,