Add support for the SO_TXTIME sockopt and SCM_TXTIME control message

CHANGELOG.md

@@ -25,6 +25,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   (#[1547](https://github.com/nix-rust/nix/pull/1547))
 - Added getter methods to `MqAttr` struct
   (#[1619](https://github.com/nix-rust/nix/pull/1619))
+- Added the `TxTime` sockopt and control message.
+  (#[1564](https://github.com/nix-rust/nix/pull/1564))
 
 ### Changed
 ### Fixed

src/sys/socket/mod.rs

@@ -1056,6 +1056,14 @@ pub enum ControlMessage<'a> {
     #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
     #[cfg_attr(docsrs, doc(cfg(all())))]
     RxqOvfl(&'a u32),
+
+    /// Configure the transmission time of packets.
+    ///
+    /// For further information, please refer to the
+    /// [`tc-etf(8)`](https://man7.org/linux/man-pages/man8/tc-etf.8.html) man
+    /// page.
+    #[cfg(target_os = "linux")]
+    TxTime(&'a u64),
 }
 
 // An opaque structure used to prevent cmsghdr from being a public type
@@ -1153,6 +1161,10 @@ impl<'a> ControlMessage<'a> {
             ControlMessage::RxqOvfl(drop_count) => {
                 drop_count as *const _ as *const u8
             },
+            #[cfg(target_os = "linux")]
+            ControlMessage::TxTime(tx_time) => {
+                tx_time as *const _ as *const u8
+            },
         };
         unsafe {
             ptr::copy_nonoverlapping(
@@ -1208,6 +1220,10 @@ impl<'a> ControlMessage<'a> {
             ControlMessage::RxqOvfl(drop_count) => {
                 mem::size_of_val(drop_count)
             },
+            #[cfg(target_os = "linux")]
+            ControlMessage::TxTime(tx_time) => {
+                mem::size_of_val(tx_time)
+            },
         }
     }
 
@@ -1237,6 +1253,8 @@ impl<'a> ControlMessage<'a> {
             ControlMessage::Ipv6PacketInfo(_) => libc::IPPROTO_IPV6,
             #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
             ControlMessage::RxqOvfl(_) => libc::SOL_SOCKET,
+            #[cfg(target_os = "linux")]
+            ControlMessage::TxTime(_) => libc::SOL_SOCKET,
         }
     }
 
@@ -1279,6 +1297,10 @@ impl<'a> ControlMessage<'a> {
             ControlMessage::RxqOvfl(_) => {
                 libc::SO_RXQ_OVFL
             },
+            #[cfg(target_os = "linux")]
+            ControlMessage::TxTime(_) => {
+                libc::SCM_TXTIME
+            },
         }
     }
 

src/sys/socket/sockopt.rs

@@ -582,6 +582,11 @@ sockopt_impl!(
     #[allow(missing_docs)]
     // Not documented by Linux!
     UdpGroSegment, Both, libc::IPPROTO_UDP, libc::UDP_GRO, bool);
+#[cfg(target_os = "linux")]
+sockopt_impl!(
+    /// Configures the behavior of time-based transmission of packets, for use
+    /// with the `TxTime` control message.
+    TxTime, Both, libc::SOL_SOCKET, libc::SO_TXTIME, libc::sock_txtime);
 #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
 sockopt_impl!(
     /// Indicates that an unsigned 32-bit value ancillary message (cmsg) should

test/sys/test_socket.rs

@@ -1997,3 +1997,60 @@ mod linux_errqueue {
         assert_eq!(ext_err.ee_info, 0);
     }
 }
+
+// Disable the test on emulated platforms because it fails in Cirrus-CI.  Lack
+// of QEMU support is suspected.
+#[cfg_attr(qemu, ignore)]
+#[cfg(target_os = "linux")]
+#[test]
+pub fn test_txtime() {
+    use nix::sys::socket::{
+        bind, recvmsg, sendmsg, setsockopt, socket, sockopt, ControlMessage,
+        MsgFlags, SockFlag, SockType,
+    };
+    use nix::sys::time::TimeValLike;
+    use nix::time::{ClockId, clock_gettime};
+
+    require_kernel_version!(test_txtime, ">= 5.8");
+
+    let std_sa = SocketAddr::from_str("127.0.0.1:6790").unwrap();
+    let inet_addr = InetAddr::from_std(&std_sa);
+    let sock_addr = SockAddr::new_inet(inet_addr);
+
+    let ssock = socket(
+        AddressFamily::Inet,
+        SockType::Datagram,
+        SockFlag::empty(),
+        None,
+    )
+    .expect("send socket failed");
+
+    let txtime_cfg = libc::sock_txtime {
+        clockid: libc::CLOCK_MONOTONIC,
+        flags: 0,
+    };
+    setsockopt(ssock, sockopt::TxTime, &txtime_cfg).unwrap();
+
+    let rsock = socket(
+        AddressFamily::Inet,
+        SockType::Datagram,
+        SockFlag::empty(),
+        None,
+    )
+    .unwrap();
+    bind(rsock, &sock_addr).unwrap();
+
+    let sbuf = [0u8; 2048];
+    let iov1 = [nix::sys::uio::IoVec::from_slice(&sbuf)];
+
+    let now = clock_gettime(ClockId::CLOCK_MONOTONIC).unwrap();
+    let delay = std::time::Duration::from_secs(1).into();
+    let txtime = (now + delay).num_nanoseconds() as u64;
+
+    let cmsg = ControlMessage::TxTime(&txtime);
+    sendmsg(ssock, &iov1, &[cmsg], MsgFlags::empty(), Some(&sock_addr)).unwrap();
+
+    let mut rbuf = [0u8; 2048];
+    let iov2 = [nix::sys::uio::IoVec::from_mut_slice(&mut rbuf)];
+    recvmsg(rsock, &iov2, None, MsgFlags::empty()).unwrap();
+}