2075: Add ControlMessage::Ipv6HopLimit

When sending IPv6 packets with `sendmsg`, Linux does not use the hop limit
set on the socket. Instead, the hop limit has to be specified for each
individual message with ancillary data in a cmsg.

This commit adds the enum variant
`ControlMessage::Ipv6HopLimit` to specify the limit.

Author: sgasse

CHANGELOG.md

@@ -21,6 +21,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Added `SOF_TIMESTAMPING_OPT_ID` and `SOF_TIMESTAMPING_OPT_TSONLY` to `nix::sys::socket::TimestampingFlag`.
   ([#2048](https://github.com/nix-rust/nix/pull/2048))
 - Enabled socket timestamping options on Android. ([#2077](https://github.com/nix-rust/nix/pull/2077))
+- Added `Ipv6HopLimit` to `::nix::sys::socket::ControlMessage` for linux.
+  ([#2074](https://github.com/nix-rust/nix/pull/2074))
 
 ### Changed
 

src/sys/socket/mod.rs

@@ -1116,7 +1116,7 @@ pub enum ControlMessage<'a> {
     #[cfg_attr(docsrs, doc(cfg(feature = "net")))]
     UdpGsoSegments(&'a u16),
 
-    /// Configure the sending addressing and interface for v4
+    /// Configure the sending addressing and interface for v4.
     ///
     /// For further information, please refer to the
     /// [`ip(7)`](https://man7.org/linux/man-pages/man7/ip.7.html) man page.
@@ -1129,7 +1129,7 @@ pub enum ControlMessage<'a> {
     #[cfg_attr(docsrs, doc(cfg(feature = "net")))]
     Ipv4PacketInfo(&'a libc::in_pktinfo),
 
-    /// Configure the sending addressing and interface for v6
+    /// Configure the sending addressing and interface for v6.
     ///
     /// For further information, please refer to the
     /// [`ipv6(7)`](https://man7.org/linux/man-pages/man7/ipv6.7.html) man page.
@@ -1154,6 +1154,17 @@ pub enum ControlMessage<'a> {
     #[cfg_attr(docsrs, doc(cfg(feature = "net")))]
     Ipv4SendSrcAddr(&'a libc::in_addr),
 
+    /// Configure the hop limit for v6 multicast traffic.
+    ///
+    /// Set the IPv6 hop limit for this message. The argument is an integer
+    /// between 0 and 255. A value of -1 will set the hop limit to the route
+    /// default if possible on the interface. Without this cmsg,  packets sent
+    /// with sendmsg have a hop limit of 1 and will not leave the local network.
+    /// For further information, please refer to the
+    /// [`ipv6(7)`](https://man7.org/linux/man-pages/man7/ipv6.7.html) man page.
+    #[cfg(any(target_os = "linux"))]
+    Ipv6HopLimit(&'a libc::c_int),
+
     /// SO_RXQ_OVFL indicates that an unsigned 32 bit value
     /// ancilliary msg (cmsg) should be attached to recieved
     /// skbs indicating the number of packets dropped by the
@@ -1267,6 +1278,8 @@ impl<'a> ControlMessage<'a> {
                       target_os = "openbsd", target_os = "dragonfly"))]
             #[cfg(feature = "net")]
             ControlMessage::Ipv4SendSrcAddr(addr) => addr as *const _ as *const u8,
+            #[cfg(any(target_os = "linux"))]
+            ControlMessage::Ipv6HopLimit(limit) => limit as *const _ as *const u8,
             #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
             ControlMessage::RxqOvfl(drop_count) => {
                 drop_count as *const _ as *const u8
@@ -1330,6 +1343,10 @@ impl<'a> ControlMessage<'a> {
                       target_os = "openbsd", target_os = "dragonfly"))]
             #[cfg(feature = "net")]
             ControlMessage::Ipv4SendSrcAddr(addr) => mem::size_of_val(addr),
+            #[cfg(any(target_os = "linux"))]
+            ControlMessage::Ipv6HopLimit(limit) => {
+                mem::size_of_val(limit)
+            },
             #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
             ControlMessage::RxqOvfl(drop_count) => {
                 mem::size_of_val(drop_count)
@@ -1369,6 +1386,9 @@ impl<'a> ControlMessage<'a> {
                       target_os = "openbsd", target_os = "dragonfly"))]
             #[cfg(feature = "net")]
             ControlMessage::Ipv4SendSrcAddr(_) => libc::IPPROTO_IP,
+            #[cfg(any(target_os = "linux"))]
+            #[cfg(feature = "net")]
+            ControlMessage::Ipv6HopLimit(_) => libc::IPPROTO_IPV6,
             #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
             ControlMessage::RxqOvfl(_) => libc::SOL_SOCKET,
             #[cfg(target_os = "linux")]
@@ -1415,6 +1435,8 @@ impl<'a> ControlMessage<'a> {
                       target_os = "openbsd", target_os = "dragonfly"))]
             #[cfg(feature = "net")]
             ControlMessage::Ipv4SendSrcAddr(_) => libc::IP_SENDSRCADDR,
+            #[cfg(any(target_os = "linux"))]
+            ControlMessage::Ipv6HopLimit(_) => libc::IPV6_HOPLIMIT,
             #[cfg(any(target_os = "android", target_os = "fuchsia", target_os = "linux"))]
             ControlMessage::RxqOvfl(_) => {
                 libc::SO_RXQ_OVFL
@@ -2240,13 +2262,7 @@ pub fn recvfrom<T: SockaddrLike>(
             &mut len as *mut socklen_t,
         ))? as usize;
 
-        Ok((
-            ret,
-            T::from_raw(
-                addr.assume_init().as_ptr(),
-                Some(len),
-            ),
-        ))
+        Ok((ret, T::from_raw(addr.assume_init().as_ptr(), Some(len))))
     }
 }