1 files changed, 79 insertions, 0 deletions
diff --git a/src/runner/sys.rs b/src/runner/sys.rs
new file mode 100644
index 0000000..b6a9428
--- /dev/null
+++ b/src/runner/sys.rs
@@ -0,0 +1,79 @@
+use crate::runner::prelude::*;
+
+const PID0: nix::unistd::Pid = nix::unistd::Pid::from_raw(0);
+
+pub fn pipe() -> Result<(std::fs::File, std::fs::File)> {
+    let (r, w) = nix::unistd::pipe2(nix::fcntl::OFlag::O_CLOEXEC)?;
+    // Safety: these file descriptors were just returned by pipe2 above, and
+    // are only available in this function, so nothing else can be accessing
+    // them
+    Ok((unsafe { std::fs::File::from_raw_fd(r) }, unsafe {
+        std::fs::File::from_raw_fd(w)
+    }))
+}
+
+pub fn set_foreground_pg(pg: nix::unistd::Pid) -> Result<()> {
+    let pty = nix::fcntl::open(
+        "/dev/tty",
+        nix::fcntl::OFlag::empty(),
+        nix::sys::stat::Mode::empty(),
+    )?;
+
+    // if a background process calls tcsetpgrp, the kernel will send it
+    // SIGTTOU which suspends it. if that background process is the session
+    // leader and doesn't have SIGTTOU blocked, the kernel will instead just
+    // return ENOTTY from the tcsetpgrp call rather than sending a signal to
+    // avoid deadlocking the process. therefore, we need to ensure that
+    // SIGTTOU is blocked here.
+
+    // Safety: setting a signal handler to SigIgn is always safe
+    unsafe {
+        nix::sys::signal::signal(
+            nix::sys::signal::Signal::SIGTTOU,
+            nix::sys::signal::SigHandler::SigIgn,
+        )?;
+    }
+    let res = nix::unistd::tcsetpgrp(pty, pg);
+    // Safety: setting a signal handler to SigDfl is always safe
+    unsafe {
+        nix::sys::signal::signal(
+            nix::sys::signal::Signal::SIGTTOU,
+            nix::sys::signal::SigHandler::SigDfl,
+        )?;
+    }
+    res?;
+
+    nix::unistd::close(pty)?;
+
+    nix::sys::signal::kill(neg_pid(pg), nix::sys::signal::Signal::SIGCONT)
+        // the process group has already exited
+        .allow(nix::errno::Errno::ESRCH)?;
+
+    Ok(())
+}
+
+pub fn setpgid_child(pg: Option<nix::unistd::Pid>) -> std::io::Result<()> {
+    nix::unistd::setpgid(PID0, pg.unwrap_or(PID0))?;
+    Ok(())
+}
+
+pub fn setpgid_parent(
+    pid: nix::unistd::Pid,
+    pg: Option<nix::unistd::Pid>,
+) -> Result<()> {
+    nix::unistd::setpgid(pid, pg.unwrap_or(PID0))
+        // the child already called exec, so it must have already called
+        // setpgid itself
+        .allow(nix::errno::Errno::EACCES)
+        // the child already exited, so we don't care
+        .allow(nix::errno::Errno::ESRCH)?;
+    Ok(())
+}
+
+pub fn id_to_pid(id: u32) -> nix::unistd::Pid {
+    nix::unistd::Pid::from_raw(id.try_into().unwrap())
+}
+
+pub fn neg_pid(pid: nix::unistd::Pid) -> nix::unistd::Pid {
+    nix::unistd::Pid::from_raw(-pid.as_raw())
+}