Make sure private_file does not get closed by rusts borrow checker

src/main.rs

@@ -21,7 +21,7 @@ fn main() {
 
     let sync_fd: c_int = args[1]
         .parse()
-        .expect("Please provide a valid file descriptor as first argument");
+        .expect("Please provide a valid file descriptor as second argument");
 
     let shared_memory = unsafe {
         mmap(
@@ -51,12 +51,11 @@ fn main() {
         .read(true)
         .write(true)
         .open(&args[2])
-        .expect("Cannot open KEY_FILE")
-        .as_raw_fd()
-        .try_into()
-        .unwrap();
+        .expect("Cannot open KEY_FILE");
 
     unsafe {
-        agent_start(shared_memory, sync_memory, private_file);
+        agent_start(shared_memory, sync_memory, private_file.as_raw_fd().try_into().unwrap());
     }
+
+    drop(private_file); // don't drop (and close) private file before here
 }