Add a method to set the controlling tty of child processes (unix).

src/libstd/sys/unix/ext/process.rs

@@ -36,14 +36,18 @@ pub trait CommandExt {
     /// that the child is the leader of a new process group. The parent process
     /// remains the child reaper of the new process.
     ///
+    /// If the tty argument is not `None`, this file will be the controlling
+    /// terminal for the new session (cf. `login_tty(3)` and tty_ioctl(4),
+    /// specifically the section on `TIOCSCTTY`). Note that this does not set
+    /// that file to be the stdio handles for the child process, to do that you
+    /// must set them directly with the `stdin()` et al methods.
+    ///
     /// This is not enough to create a daemon process. The *init* process should
     /// be the child reaper of a daemon. This can be achieved if the parent
     /// process exit. Moreover, a daemon should not have a controlling terminal.
-    /// To achieve this, a session leader (the child) must spawn another process
-    /// (the daemon) in the same session.
     #[unstable(feature = "process_session_leader", reason = "recently added",
                issue = "27811")]
-    fn session_leader(&mut self, on: bool) -> &mut process::Command;
+    fn session_leader<T: AsRawFd>(&mut self, tty: Option<&T>) -> &mut process::Command;
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -58,8 +62,12 @@ impl CommandExt for process::Command {
         self
     }
 
-    fn session_leader(&mut self, on: bool) -> &mut process::Command {
-        self.as_inner_mut().session_leader = on;
+    fn session_leader<T: AsRawFd>(&mut self, tty: Option<&T>) -> &mut process::Command {
+        {
+            let inner = self.as_inner_mut();
+            inner.session_leader = true;
+            inner.tty = tty.map(T::as_raw_fd);
+        }
         self
     }
 }

src/libstd/sys/unix/process.rs

@@ -37,6 +37,7 @@ pub struct Command {
     pub uid: Option<uid_t>,
     pub gid: Option<gid_t>,
     pub session_leader: bool,
+    pub tty: Option<RawFd>,
 }
 
 impl Command {
@@ -49,6 +50,7 @@ impl Command {
             uid: None,
             gid: None,
             session_leader: false,
+            tty: None,
         }
     }
 
@@ -307,7 +309,23 @@ impl Process {
             // process leader already. We just forked so it shouldn't return
             // error, but ignore it anyway.
             let _ = libc::setsid();
+
+            // Associate the tty file descriptor with the controlling terminal,
+            // then close it unless it is an stdio handle. Errors returned by
+            // close are ignored.
+            if let Some(tty) = cfg.tty {
+
+                const TIOCSCTTY: u64 = 0x540E;
+
+                if cvt_r(|| libc::funcs::bsd44::ioctl(tty, TIOCSCTTY)).is_err() {
+                    fail(&mut output);
+                } else if tty > 2 {
+                    let _ = libc::close(tty);
+                }
+
+            }
         }
+
         if !dirp.is_null() && libc::chdir(dirp) == -1 {
             fail(&mut output);
         }