Merge recent update from ch7 && cargo clippy

user/src/bin/initproc.rs

@@ -1,7 +1,6 @@
 #![no_std]
 #![no_main]
 
-#[macro_use]
 extern crate user_lib;
 
 use user_lib::{
@@ -14,7 +13,7 @@ use user_lib::{
 #[no_mangle]
 fn main() -> i32 {
     if fork() == 0 {
-        exec("user_shell\0", &[0 as *const u8]);
+        exec("user_shell\0", &[core::ptr::null::<u8>()]);
     } else {
         loop {
             let mut exit_code: i32 = 0;
@@ -23,11 +22,13 @@ fn main() -> i32 {
                 yield_();
                 continue;
             }
+            /*
             println!(
                 "[initproc] Released a zombie process, pid={}, exit_code={}",
                 pid,
                 exit_code,
             );
+            */
         }
     }
     0