Implement sys_read && allocate pid and kernel stack dynamically.

os/src/syscall/fs.rs

@@ -1,6 +1,8 @@
 use crate::mm::translated_byte_buffer;
-use crate::task::current_user_token;
+use crate::task::{current_user_token, suspend_current_and_run_next};
+use crate::sbi::console_getchar;
 
+const FD_STDIN: usize = 0;
 const FD_STDOUT: usize = 1;
 
 pub fn sys_write(fd: usize, buf: *const u8, len: usize) -> isize {
@@ -16,4 +18,29 @@ pub fn sys_write(fd: usize, buf: *const u8, len: usize) -> isize {
             panic!("Unsupported fd in sys_write!");
         }
     }
+}
+
+pub fn sys_read(fd: usize, buf: *const u8, len: usize) -> isize {
+    match fd {
+        FD_STDIN => {
+            assert_eq!(len, 1, "Only support len = 1 in sys_read!");
+            let mut c: usize;
+            loop {
+                c = console_getchar();
+                if c == 0 {
+                    suspend_current_and_run_next();
+                    continue;
+                } else {
+                    break;
+                }
+            }
+            let ch = c as u8;
+            let mut buffers = translated_byte_buffer(current_user_token(), buf, len);
+            unsafe { buffers[0].as_mut_ptr().write_volatile(ch); }
+            1
+        }
+        _ => {
+            panic!("Unsupported fd in sys_read!");
+        }
+    }
 }