virtio-devices, vmm: vhost: net: Add client mode support

Adding the support for an OVS vhost-user backend to connect as the
vhost-user client. This means we introduce with this patch a new
option to our `--net` parameter. This option is called 'server' in order
to ask the VMM to run as the server for the vhost-user socket.

Fixes #1745

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

virtio-devices/src/vhost_user/mod.rs

@@ -24,10 +24,14 @@ pub use self::vu_common_ctrl::VhostUserConfig;
 
 #[derive(Debug)]
 pub enum Error {
+    /// Failed accepting connection.
+    AcceptConnection(io::Error),
     /// Invalid available address.
     AvailAddress,
     /// Queue number  is not correct
     BadQueueNum,
+    /// Failed binding vhost-user socket.
+    BindSocket(io::Error),
     /// Creating kill eventfd failed.
     CreateKillEventFd(io::Error),
     /// Cloning kill eventfd failed.

virtio-devices/src/vhost_user/net.rs

@@ -16,6 +16,7 @@ use net_util::MacAddr;
 use seccomp::{SeccompAction, SeccompFilter};
 use std::ops::Deref;
 use std::os::unix::io::AsRawFd;
+use std::os::unix::net::UnixListener;
 use std::result;
 use std::sync::{Arc, Barrier};
 use std::thread;
@@ -46,6 +47,7 @@ pub struct Net {
     seccomp_action: SeccompAction,
     guest_memory: Option<GuestMemoryAtomic<GuestMemoryMmap>>,
     acked_protocol_features: u64,
+    socket_path: Option<String>,
 }
 
 impl Net {
@@ -56,9 +58,23 @@ impl Net {
         mac_addr: MacAddr,
         vu_cfg: VhostUserConfig,
         seccomp_action: SeccompAction,
+        server: bool,
     ) -> Result<Net> {
-        let mut vhost_user_net = Master::connect(&vu_cfg.socket, vu_cfg.num_queues as u64)
-            .map_err(Error::VhostUserCreateMaster)?;
+        let mut socket_path: Option<String> = None;
+
+        let mut vhost_user_net = if server {
+            info!("Binding vhost-user-net listener...");
+            let listener = UnixListener::bind(&vu_cfg.socket).map_err(Error::BindSocket)?;
+            info!("Waiting for incoming vhost-user-net connection...");
+            let (stream, _) = listener.accept().map_err(Error::AcceptConnection)?;
+
+            socket_path = Some(vu_cfg.socket.clone());
+
+            Master::from_stream(stream, vu_cfg.num_queues as u64)
+        } else {
+            Master::connect(&vu_cfg.socket, vu_cfg.num_queues as u64)
+                .map_err(Error::VhostUserCreateMaster)?
+        };
 
         // Filling device and vring features VMM supports.
         let mut avail_features = 1 << virtio_net::VIRTIO_NET_F_GUEST_CSUM
@@ -166,6 +182,7 @@ impl Net {
             seccomp_action,
             guest_memory: None,
             acked_protocol_features,
+            socket_path,
         })
     }
 }
@@ -368,6 +385,11 @@ impl VirtioDevice for Net {
 
     fn shutdown(&mut self) {
         let _ = unsafe { libc::close(self.vhost_user_net.as_raw_fd()) };
+
+        // Remove socket path if needed
+        if let Some(socket_path) = &self.socket_path {
+            let _ = std::fs::remove_file(socket_path);
+        }
     }
 
     fn add_memory_region(