diff --git a/user/ucore-ulib/src/syscall.rs b/user/ucore-ulib/src/syscall.rs
index 1a75785..da3ae5d 100644
--- a/user/ucore-ulib/src/syscall.rs
+++ b/user/ucore-ulib/src/syscall.rs
@@ -44,7 +44,8 @@ impl fmt::Write for SysPutc {
 }
 
 #[inline(always)]
-fn sys_call(id: usize, arg0: usize, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) -> i32 {
+fn sys_call(syscall_id: SyscallId, arg0: usize, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) -> i32 {
+    let id = syscall_id as usize;
     let ret: i32;
     unsafe {
         #[cfg(target_arch = "riscv32")]
@@ -70,12 +71,12 @@ fn sys_call(id: usize, arg0: usize, arg1: usize, arg2: usize, arg3: usize, arg4:
 }
 
 pub fn sys_exit(code: usize) -> ! {
-    sys_call(SYS_EXIT, code, 0, 0, 0, 0, 0);
+    sys_call(SyscallId::Exit, code, 0, 0, 0, 0, 0);
     unreachable!()
 }
 
 pub fn sys_write(fd: usize, base: *const u8, len: usize) -> i32 {
-    sys_call(SYS_WRITE, fd, base as usize, len, 0, 0, 0)
+    sys_call(SyscallId::Write, fd, base as usize, len, 0, 0, 0)
 }
 
 pub fn sys_open(path: &str, flags: usize) -> i32 {
@@ -83,86 +84,89 @@ pub fn sys_open(path: &str, flags: usize) -> i32 {
     use core::mem::replace;
     let end = unsafe { &mut *(path.as_ptr().offset(path.len() as isize) as *mut u8) };
     let backup = replace(end, 0);
-    let ret = sys_call(SYS_OPEN, path.as_ptr() as usize, flags, 0, 0, 0, 0);
+    let ret = sys_call(SyscallId::Open, path.as_ptr() as usize, flags, 0, 0, 0, 0);
     *end = backup;
     ret
 }
 
 pub fn sys_close(fd: usize) -> i32 {
-    sys_call(SYS_CLOSE, fd, 0, 0, 0, 0, 0)
+    sys_call(SyscallId::Close, fd, 0, 0, 0, 0, 0)
 }
 
 pub fn sys_dup(fd1: usize, fd2: usize) -> i32 {
-    sys_call(SYS_DUP, fd1, fd2, 0, 0, 0, 0)
+    sys_call(SyscallId::Dup, fd1, fd2, 0, 0, 0, 0)
 }
 
 /// Fork the current process. Return the child's PID.
 pub fn sys_fork() -> i32 {
-    sys_call(SYS_FORK, 0, 0, 0, 0, 0, 0)
+    sys_call(SyscallId::Fork, 0, 0, 0, 0, 0, 0)
 }
 
 /// Wait the process exit.
 /// Return the PID. Store exit code to `code` if it's not null.
 pub fn sys_wait(pid: usize, code: *mut i32) -> i32 {
-    sys_call(SYS_WAIT, pid, code as usize, 0, 0, 0, 0)
+    sys_call(SyscallId::Wait, pid, code as usize, 0, 0, 0, 0)
 }
 
 pub fn sys_yield() -> i32 {
-    sys_call(SYS_YIELD, 0, 0, 0, 0, 0, 0)
+    sys_call(SyscallId::Yield, 0, 0, 0, 0, 0, 0)
 }
 
 /// Kill the process
 pub fn sys_kill(pid: usize) -> i32 {
-    sys_call(SYS_KILL, pid, 0, 0, 0, 0, 0)
+    sys_call(SyscallId::Kill, pid, 0, 0, 0, 0, 0)
 }
 
 /// Get the current process id
 pub fn sys_getpid() -> i32 {
-    sys_call(SYS_GETPID, 0, 0, 0, 0, 0, 0)
+    sys_call(SyscallId::GetPid, 0, 0, 0, 0, 0, 0)
 }
 
 pub fn sys_sleep(time: usize) -> i32 {
-    sys_call(SYS_SLEEP, time, 0, 0, 0, 0, 0)
+    sys_call(SyscallId::Sleep, time, 0, 0, 0, 0, 0)
 }
 
 pub fn sys_get_time() -> i32 {
-    sys_call(SYS_GETTIME, 0, 0, 0, 0, 0, 0)
+    sys_call(SyscallId::GetTime, 0, 0, 0, 0, 0, 0)
 }
 
 pub fn sys_lab6_set_priority(priority: usize) -> i32 {
-    sys_call(SYS_LAB6_SET_PRIORITY, priority, 0, 0, 0, 0, 0)
+    sys_call(SyscallId::Lab6SetPriority, priority, 0, 0, 0, 0, 0)
 }
 
 pub fn sys_putc(c: char) -> i32 {
-    sys_call(SYS_PUTC, c as usize, 0, 0, 0, 0, 0)
-}
-
-const SYS_EXIT: usize = 1;
-const SYS_FORK: usize = 2;
-const SYS_WAIT: usize = 3;
-const SYS_EXEC: usize = 4;
-const SYS_CLONE: usize = 5;
-const SYS_YIELD: usize = 10;
-const SYS_SLEEP: usize = 11;
-const SYS_KILL: usize = 12;
-const SYS_GETTIME: usize = 17;
-const SYS_GETPID: usize = 18;
-const SYS_MMAP: usize = 20;
-const SYS_MUNMAP: usize = 21;
-const SYS_SHMEM: usize = 22;
-const SYS_PUTC: usize = 30;
-const SYS_PGDIR: usize = 31;
-const SYS_OPEN: usize = 100;
-const SYS_CLOSE: usize = 101;
-const SYS_READ: usize = 102;
-const SYS_WRITE: usize = 103;
-const SYS_SEEK: usize = 104;
-const SYS_FSTAT: usize = 110;
-const SYS_FSYNC: usize = 111;
-const SYS_GETCWD: usize = 121;
-const SYS_GETDIRENTRY: usize = 128;
-const SYS_DUP: usize = 130;
-const SYS_LAB6_SET_PRIORITY: usize = 255;
+    sys_call(SyscallId::Putc, c as usize, 0, 0, 0, 0, 0)
+}
+
+#[allow(dead_code)]
+enum SyscallId{
+    Exit = 1,
+    Fork = 2,
+    Wait = 3,
+    Exec = 4,
+    Clone = 5,
+    Yield = 10,
+    Sleep = 11,
+    Kill = 12,
+    GetTime = 17,
+    GetPid = 18,
+    Mmap = 20,
+    Munmap = 21,
+    Shmem = 22,
+    Putc = 30,
+    Pgdir = 31,
+    Open = 100,
+    Close = 101,
+    Read = 102,
+    Write = 103,
+    Seek = 104,
+    Fstat = 110,
+    Fsync = 111,
+    GetCwd = 121,
+    GetDirEntry = 128,
+    Dup = 130,
+    Lab6SetPriority = 255,
+}
 
 /* VFS flags */
 // TODO: use bitflags