forktree worked with depth=3 on k210 platform.

user/src/bin/forktree.rs

@@ -0,0 +1,37 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+
+use user_lib::{sleep, getpid, fork, exit, yield_};
+
+const DEPTH: usize = 3;
+
+fn fork_child(cur: &str, branch: char) {
+    let mut next = [0u8; DEPTH + 1];
+    let l = cur.len();
+    if l >= DEPTH {
+        return;
+    }
+    &mut next[..l].copy_from_slice(cur.as_bytes());
+    next[l] = branch as u8;
+    if fork() == 0 {
+        fork_tree(core::str::from_utf8(&next[..l + 1]).unwrap());
+        yield_();
+        exit(0);
+    }
+}
+
+fn fork_tree(cur: &str) {
+    println!("pid{}: {}", getpid(), cur);
+    fork_child(cur, '0');
+    fork_child(cur, '1');
+}
+
+#[no_mangle]
+pub fn main() -> i32 {
+    fork_tree("");
+    sleep(3000);
+    0
+}