Handle backspace for k210/qemu platform && Add lots of user tests.

user/src/bin/forktest2.rs

@@ -0,0 +1,35 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+
+use user_lib::{fork, wait, get_time, getpid, exit, yield_,};
+
+static NUM: usize = 13;
+
+#[no_mangle]
+pub fn main() -> i32 {
+    for _ in 0..NUM {
+        let pid = fork();
+        if pid == 0 {
+            let current_time = get_time();
+            let sleep_length = (current_time as i32 as isize) * (current_time as i32 as isize) % 1000 + 1000;
+            println!("Subprocess {} sleep for {} ms", getpid(), sleep_length);
+            while get_time() < current_time + sleep_length {
+                yield_();
+            }
+            println!("Subprocess {} OK!", getpid());
+            exit(0);
+        }
+    }
+
+    let mut xstate: i32 = 0;
+    for _ in 0..NUM {
+        assert!(wait(&mut xstate) > 0);
+        assert_eq!(xstate, 0);
+    }
+    assert!(wait(&mut xstate) < 0);
+    println!("r_forktest2 test passed!");
+    0
+}