feat(vmm): add tap device creation

This adds the automatic creation of a tap network interface on the host
when a VMM is started. Those network interfaces are named `tapletX`.

Two new CLI arguments were added to configure this interface, `--network-host-ip`
and `--network-host-netmask`, which configures the IP address of the tap
interface on the host side.

Code was taken and adapted from the [cloud-hypervisor project](https://github.com/cloud-hypervisor/cloud-hypervisor/tree/main/net_util/src).

Signed-off-by: Kuruyia <github@kuruyia.net>

src/vmm/Cargo.toml

@@ -20,6 +20,7 @@ linux-loader = { version = "0.11.0", features = ["bzimage", "elf"] }
 log = "0.4.20"
 tracing = "0.1.40"
 tracing-subscriber = "0.3.18"
+virtio-bindings = "0.2.2"
 vm-device = "0.1.0"
 vm-memory = { version = "0.14.0", features = ["backend-mmap"] }
 vm-superio = "0.7.0"

src/vmm/src/args.rs

@@ -1,5 +1,5 @@
 //! Command-line arguments.
-use std::path::PathBuf;
+use std::{net::Ipv4Addr, path::PathBuf};
 
 use clap::Parser;
 use clap_verbosity_flag::{InfoLevel, Verbosity};
@@ -21,6 +21,14 @@ pub struct CliArguments {
     #[clap(short, long, env, default_value = "512")]
     pub memory: u32,
 
+    /// IPv4 address of the host tap interface.
+    #[clap(long, env)]
+    pub network_host_ip: Ipv4Addr,
+
+    /// Subnet mask of the host tap interface.
+    #[clap(long, env)]
+    pub network_host_netmask: Ipv4Addr,
+
     /// Verbosity level.
     #[command(flatten)]
     pub verbose: Verbosity<InfoLevel>,

src/vmm/src/core/mod.rs

@@ -8,10 +8,13 @@ extern crate vm_superio;
 use linux_loader::loader;
 use std::io;
 
+use self::network::open_tap;
+
 mod cpu;
 mod devices;
 mod epoll_context;
 mod kernel;
+mod network;
 pub mod vmm;
 
 #[derive(Debug)]
@@ -48,6 +51,8 @@ pub enum Error {
     StdinWrite(vm_superio::serial::Error<io::Error>),
     /// Terminal configuration error
     TerminalConfigure(kvm_ioctls::Error),
+    // Tap open error
+    OpenTap(open_tap::Error),
 }
 
 /// Dedicated [`Result`](https://doc.rust-lang.org/std/result/) type.

src/vmm/src/core/network/mac.rs

@@ -0,0 +1,100 @@
+// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+//
+// Portions Copyright 2017 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the THIRD-PARTY file.
+
+use std::fmt;
+use std::io;
+use std::str::FromStr;
+
+pub const MAC_ADDR_LEN: usize = 6;
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct MacAddr {
+    bytes: [u8; MAC_ADDR_LEN],
+}
+
+impl MacAddr {
+    pub fn parse_str<S>(s: &S) -> Result<MacAddr, io::Error>
+    where
+        S: AsRef<str> + ?Sized,
+    {
+        let v: Vec<&str> = s.as_ref().split(':').collect();
+        let mut bytes = [0u8; MAC_ADDR_LEN];
+        let common_err = Err(io::Error::new(
+            io::ErrorKind::Other,
+            format!("parsing of {} into a MAC address failed", s.as_ref()),
+        ));
+
+        if v.len() != MAC_ADDR_LEN {
+            return common_err;
+        }
+
+        for i in 0..MAC_ADDR_LEN {
+            if v[i].len() != 2 {
+                return common_err;
+            }
+            bytes[i] = u8::from_str_radix(v[i], 16).map_err(|e| {
+                io::Error::new(
+                    io::ErrorKind::Other,
+                    format!("parsing of {} into a MAC address failed: {}", s.as_ref(), e),
+                )
+            })?;
+        }
+
+        Ok(MacAddr { bytes })
+    }
+
+    // Does not check whether src.len() == MAC_ADDR_LEN.
+    #[inline]
+    pub fn from_bytes_unchecked(src: &[u8]) -> MacAddr {
+        // TODO: using something like std::mem::uninitialized could avoid the extra initialization,
+        // if this ever becomes a performance bottleneck.
+        let mut bytes = [0u8; MAC_ADDR_LEN];
+        bytes[..].copy_from_slice(src);
+
+        MacAddr { bytes }
+    }
+
+    // An error can only occur if the slice length is different from MAC_ADDR_LEN.
+    #[inline]
+    pub fn from_bytes(src: &[u8]) -> Result<MacAddr, io::Error> {
+        if src.len() != MAC_ADDR_LEN {
+            return Err(io::Error::new(
+                io::ErrorKind::Other,
+                format!("invalid length of slice: {} vs {}", src.len(), MAC_ADDR_LEN),
+            ));
+        }
+        Ok(MacAddr::from_bytes_unchecked(src))
+    }
+
+    #[inline]
+    pub fn get_bytes(&self) -> &[u8] {
+        &self.bytes
+    }
+}
+
+impl fmt::Display for MacAddr {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let b = &self.bytes;
+        write!(
+            f,
+            "{:02x}:{:02x}:{:02x}:{:02x}:{:02x}:{:02x}",
+            b[0], b[1], b[2], b[3], b[4], b[5]
+        )
+    }
+}
+
+pub enum MacAddrParseError {
+    InvalidValue(String),
+}
+
+impl FromStr for MacAddr {
+    type Err = MacAddrParseError;
+
+    fn from_str(s: &str) -> std::result::Result<Self, Self::Err> {
+        MacAddr::parse_str(s).map_err(|_| MacAddrParseError::InvalidValue(s.to_owned()))
+    }
+}

src/vmm/src/core/network/mod.rs

@@ -0,0 +1,63 @@
+// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+//
+// Portions Copyright 2017 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the THIRD-PARTY file.
+
+use std::{io, mem, net, os::fd::FromRawFd};
+
+use virtio_bindings::virtio_net::virtio_net_hdr_v1;
+
+pub(crate) mod mac;
+pub(crate) mod net_gen;
+pub(crate) mod open_tap;
+pub(crate) mod tap;
+
+#[derive(Debug)]
+pub enum Error {
+    CreateSocket(io::Error),
+}
+
+/// Create a sockaddr_in from an IPv4 address, and expose it as
+/// an opaque sockaddr suitable for usage by socket ioctls.
+fn create_sockaddr(ip_addr: net::Ipv4Addr) -> net_gen::sockaddr {
+    // IPv4 addresses big-endian (network order), but Ipv4Addr will give us
+    // a view of those bytes directly so we can avoid any endian trickiness.
+    let addr_in = net_gen::sockaddr_in {
+        sin_family: net_gen::AF_INET as u16,
+        sin_port: 0,
+        // SAFETY: ip_addr can be safely transmute to in_addr
+        sin_addr: unsafe { mem::transmute(ip_addr.octets()) },
+        __pad: [0; 8usize],
+    };
+
+    // SAFETY: addr_in can be safely transmute to sockaddr
+    unsafe { mem::transmute(addr_in) }
+}
+
+fn create_inet_socket() -> Result<net::UdpSocket, Error> {
+    // SAFETY: we check the return value.
+    let sock = unsafe { libc::socket(libc::AF_INET, libc::SOCK_DGRAM, 0) };
+    if sock < 0 {
+        return Err(Error::CreateSocket(io::Error::last_os_error()));
+    }
+
+    // SAFETY: nothing else will use or hold onto the raw sock fd.
+    Ok(unsafe { net::UdpSocket::from_raw_fd(sock) })
+}
+
+fn create_unix_socket() -> Result<net::UdpSocket, Error> {
+    // SAFETY: we check the return value.
+    let sock = unsafe { libc::socket(libc::AF_UNIX, libc::SOCK_DGRAM, 0) };
+    if sock < 0 {
+        return Err(Error::CreateSocket(io::Error::last_os_error()));
+    }
+
+    // SAFETY: nothing else will use or hold onto the raw sock fd.
+    Ok(unsafe { net::UdpSocket::from_raw_fd(sock) })
+}
+
+fn vnet_hdr_len() -> usize {
+    std::mem::size_of::<virtio_net_hdr_v1>()
+}