add hint for user shell. detect cores through 'SMP' env.

kernel/Makefile

@@ -34,6 +34,7 @@ bootimage := target/$(target)/bootimage.bin
 user_dir := ../user
 
 export ARCH = $(arch)
+export SMP = $(smp)
 #export SFSIMG = $(user_dir)/build/user-$(arch).img
 ifeq ($(arch), x86_64)
 export SFSIMG = $(user_dir)/img/ucore-i386.img

kernel/src/process/mod.rs

@@ -21,10 +21,13 @@ pub fn init() {
         }
     }
 
+    // Add idle threads
     extern fn idle(_arg: usize) -> ! {
         loop { cpu::halt(); }
     }
-    for i in 0..4 {
+    use core::str::FromStr;
+    let cores = usize::from_str(env!("SMP")).unwrap();
+    for i in 0..cores {
         manager.add(Process::new_kernel(idle, i), 0);
     }
     crate::shell::run_user_shell();

kernel/src/shell.rs

@@ -7,6 +7,8 @@ use crate::process::*;
 
 pub fn run_user_shell() {
     if let Ok(inode) = ROOT_INODE.lookup("sh") {
+        println!("Going to user mode shell.");
+        println!("Use 'ls' to list available programs.");
         let data = inode.read_as_vec().unwrap();
         processor().manager().add(Process::new_user(data.as_slice(), "sh".split(' ')), 0);
     } else {