let linux signal supervised mycelium when we die

1 files changed, 22 insertions, 8 deletions

diff --git a/src/transport/mycelium.rs b/src/transport/mycelium.rs
index 3a08b76..d31925d 100644
--- a/src/transport/mycelium.rs
+++ b/src/transport/mycelium.rs
@@ -269,15 +269,29 @@ impl SupervisedMycelium {
         let mut cmd = Command::new("mycelium");
 
         let fds_to_inherit: Vec<i32> = [node_fd, net_fd].iter().filter_map(|&x| x).collect();
-        if !fds_to_inherit.is_empty() {
-            unsafe {
-                cmd.pre_exec(move || {
-                    for &fd in &fds_to_inherit {
-                        libc::fcntl(fd, libc::F_SETFD, 0);
+        // The child must never outlive us. An orphaned Mycelium keeps running with our
+        // key; the next one we start then shares its address, and replies (including
+        // Mycelium's own message ACKs) go to whichever instance the routers picked,
+        // leaving our messages pending forever. Drop only runs on a clean shutdown, so
+        // let the kernel signal the child when we die, however we die.
+        let parent_pid = std::process::id() as libc::pid_t;
+        unsafe {
+            cmd.pre_exec(move || {
+                for &fd in &fds_to_inherit {
+                    libc::fcntl(fd, libc::F_SETFD, 0);
+                }
+                #[cfg(target_os = "linux")]
+                {
+                    if libc::prctl(libc::PR_SET_PDEATHSIG, libc::SIGTERM) != 0 {
+                        return Err(std::io::Error::last_os_error());
                     }
-                    Ok(())
-                });
-            }
+                    // We may have died between fork and prctl.
+                    if libc::getppid() != parent_pid {
+                        libc::_exit(1);
+                    }
+                }
+                Ok(())
+            });
         }
 
         cmd.arg("--key-file")