Auto merge of #69864 - LinkTed:master, r=Amanieu

unix: Extend UnixStream and UnixDatagram to send and receive file descriptors

Add the functions `recv_vectored_fds` and `send_vectored_fds` to `UnixDatagram` and `UnixStream`. With this functions `UnixDatagram` and `UnixStream` can send and receive file descriptors, by using `recvmsg` and `sendmsg` system call.

library/std/src/sys/unix/net.rs

@@ -275,6 +275,20 @@ impl Socket {
         self.recv_from_with_flags(buf, 0)
     }
 
+    #[cfg(any(
+        target_os = "android",
+        target_os = "dragonfly",
+        target_os = "emscripten",
+        target_os = "freebsd",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_os = "openbsd",
+    ))]
+    pub fn recv_msg(&self, msg: &mut libc::msghdr) -> io::Result<usize> {
+        let n = cvt(unsafe { libc::recvmsg(self.0.raw(), msg, libc::MSG_CMSG_CLOEXEC) })?;
+        Ok(n as usize)
+    }
+
     pub fn peek_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
         self.recv_from_with_flags(buf, MSG_PEEK)
     }
@@ -292,6 +306,20 @@ impl Socket {
         self.0.is_write_vectored()
     }
 
+    #[cfg(any(
+        target_os = "android",
+        target_os = "dragonfly",
+        target_os = "emscripten",
+        target_os = "freebsd",
+        target_os = "linux",
+        target_os = "netbsd",
+        target_os = "openbsd",
+    ))]
+    pub fn send_msg(&self, msg: &mut libc::msghdr) -> io::Result<usize> {
+        let n = cvt(unsafe { libc::sendmsg(self.0.raw(), msg, 0) })?;
+        Ok(n as usize)
+    }
+
     pub fn set_timeout(&self, dur: Option<Duration>, kind: libc::c_int) -> io::Result<()> {
         let timeout = match dur {
             Some(dur) => {
@@ -351,6 +379,17 @@ impl Socket {
         Ok(raw != 0)
     }
 
+    #[cfg(any(target_os = "android", target_os = "linux",))]
+    pub fn set_passcred(&self, passcred: bool) -> io::Result<()> {
+        setsockopt(self, libc::SOL_SOCKET, libc::SO_PASSCRED, passcred as libc::c_int)
+    }
+
+    #[cfg(any(target_os = "android", target_os = "linux",))]
+    pub fn passcred(&self) -> io::Result<bool> {
+        let passcred: libc::c_int = getsockopt(self, libc::SOL_SOCKET, libc::SO_PASSCRED)?;
+        Ok(passcred != 0)
+    }
+
     #[cfg(not(any(target_os = "solaris", target_os = "illumos")))]
     pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
         let mut nonblocking = nonblocking as libc::c_int;