login: pass shell console fds explicitly as Stdio (relibc inheritance drops login-shell stdio; getty does the same for login)

src/lib.rs

@@ -132,6 +132,36 @@ pub fn spawn_shell<T: Default>(user: &User<T>) -> IoResult<i32> {
 
     let mut command = user.shell_cmd();
 
+    // The relibc Redox spawn does not reliably carry inherited stdio (fds 0/1/2)
+    // to the child through filetable inheritance for a login shell: the fds
+    // arrive disconnected, so the shell has no console, reads EOF immediately,
+    // exits, and getty re-spawns login in a tight loop. getty itself sidesteps
+    // this by handing `login` its console fds *explicitly* as Stdio (see
+    // getty.rs), which the spawn lowers to dup2 file-actions that actually
+    // connect the child's descriptors. Do the same for the shell: duplicate the
+    // current console fds and pass them explicitly. Stdio takes ownership of the
+    // dups and closes them after the spawn; login keeps its own 0/1/2.
+    #[cfg(target_os = "redox")]
+    unsafe {
+        use std::os::fd::{FromRawFd, RawFd};
+        use std::process::Stdio;
+        let din = libc::dup(0);
+        let dout = libc::dup(1);
+        let derr = libc::dup(2);
+        if din >= 0 && dout >= 0 && derr >= 0 {
+            command
+                .stdin(Stdio::from_raw_fd(din as RawFd))
+                .stdout(Stdio::from_raw_fd(dout as RawFd))
+                .stderr(Stdio::from_raw_fd(derr as RawFd));
+        } else {
+            for d in [din, dout, derr] {
+                if d >= 0 {
+                    libc::close(d);
+                }
+            }
+        }
+    }
+
     let mut child = command.spawn()?;
     match child.wait()?.code() {
         Some(code) => Ok(code),