add user app: forkexec.rs, update hello_world.rs

user/src/bin/forkexec.rs

@@ -0,0 +1,27 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+
+use user_lib::{fork, getpid, wait, exec};
+
+#[no_mangle]
+pub fn main() -> i32 {
+    println!("pid {}: parent start forking ...", getpid());
+    let pid = fork();
+    if pid == 0 {
+        // child process
+        println!("pid {}: forked child start execing hello_world app ... ", getpid());
+        exec("hello_world");
+        100
+    } else {
+        // parent process
+        let mut exit_code: i32 = 0;
+        println!("pid {}: ready waiting child ...", getpid());
+        assert_eq!(pid, wait(&mut exit_code));
+        assert_eq!(exit_code, 0);
+        println!("pid {}: got child info:: pid {}, exit code: {}", getpid() , pid, exit_code);
+        0
+    }
+}

user/src/bin/hello_world.rs

@@ -4,8 +4,10 @@
 #[macro_use]
 extern crate user_lib;
 
+use user_lib::{getpid};
+
 #[no_mangle]
 pub fn main() -> i32 {
-    println!("Hello world from user mode program!");
+    println!("pid {}: Hello world from user mode program!", getpid());
     0
 }