diff --git a/Makefile b/Makefile
index 59d261c..8bc60d9 100644
--- a/Makefile
+++ b/Makefile
@@ -194,6 +194,7 @@ UPROGS=\
 	$U/_primes\
 	$U/_find\
 	$U/_xargs\
+	$U/_trace\
 
 
 
diff --git a/conf/lab.mk b/conf/lab.mk
index 05e8b8d..278d1a8 100644
--- a/conf/lab.mk
+++ b/conf/lab.mk
@@ -1 +1 @@
-LAB=util
+LAB=syscall
diff --git a/grade-lab-syscall b/grade-lab-syscall
new file mode 100644
index 0000000..b218cc0
--- /dev/null
+++ b/grade-lab-syscall
@@ -0,0 +1,136 @@
+#!/usr/bin/env python3
+
+import re
+from gradelib import *
+
+r = Runner(save("xv6.out"))
+
+@test(5, "answers-syscall.txt")
+def test_answers():
+    # just a simple sanity check, will be graded manually
+    check_answers("answers-syscall.txt")
+
+@test(5, "trace 32 grep")
+def test_trace_32_grep():
+    r.run_qemu(shell_script([
+        'trace 32 grep hello README'
+    ]))
+
+    sys_cnt = {
+    'read' : 0
+    }
+
+    sys_cnt['read'] += 1
+    s = r'^\d+: syscall read\(trace counts: ' + str(sys_cnt['read']) + r'\) -> 1023'
+    r.match(s)
+
+    sys_cnt['read'] += 1
+    s = r'^\d+: syscall read\(trace counts: ' + str(sys_cnt['read']) + r'\) -> 961'
+    r.match(s)
+
+    sys_cnt['read'] += 1
+    s = r'^\d+: syscall read\(trace counts: ' + str(sys_cnt['read']) + r'\) -> 321'
+    r.match(s)
+
+    sys_cnt['read'] += 1
+    s = r'^\d+: syscall read\(trace counts: ' + str(sys_cnt['read']) + r'\) -> 0'
+    r.match(s)
+
+@test(5, "trace all grep")
+def test_trace_all_grep():
+    r.run_qemu(shell_script([
+        'trace 2147483647 grep hello README'
+    ]))
+
+    sys_cnt = {
+    'read' : 0,
+    'trace' : 0,
+    'exec' : 0,
+    'open' : 0,
+    'close' : 0,
+    'fork' : 0,
+    }
+
+    sys_cnt['trace'] += 1
+    s = r'^\d+: syscall trace\(trace counts: ' + str(sys_cnt['trace']) + r'\) -> 0'
+    r.match(s)
+
+    sys_cnt['exec'] += 1
+    s = r'^\d+: syscall exec\(trace counts: ' + str(sys_cnt['exec']) + r'\) -> 3'
+    r.match(s)
+
+    sys_cnt['open'] += 1
+    s = r'^\d+: syscall open\(trace counts: ' + str(sys_cnt['open']) + r'\) -> 3'
+    r.match(s)
+
+
+    sys_cnt['read'] += 1
+    s = r'^\d+: syscall read\(trace counts: ' + str(sys_cnt['read']) + r'\) -> 1023'
+    r.match(s)
+
+    sys_cnt['read'] += 1
+    s = r'^\d+: syscall read\(trace counts: ' + str(sys_cnt['read']) + r'\) -> 961'
+    r.match(s)
+
+    sys_cnt['read'] += 1
+    s = r'^\d+: syscall read\(trace counts: ' + str(sys_cnt['read']) + r'\) -> 321'
+    r.match(s)
+
+    sys_cnt['read'] += 1
+    s = r'^\d+: syscall read\(trace counts: ' + str(sys_cnt['read']) + r'\) -> 0'
+    r.match(s)
+
+    sys_cnt['close'] += 1
+    s = r'^\d+: syscall close\(trace counts: ' + str(sys_cnt['close']) + r'\) -> 0'
+    r.match(s)
+
+@test(5, "trace nothing")
+def test_trace_nothing():
+    r.run_qemu(shell_script([
+        'grep hello README'
+    ]))
+    r.match(no=[".* syscall .*"])
+
+@test(5, "trace children")
+def test_trace_children():
+    r.run_qemu(shell_script([
+        'trace 2 usertests forkforkfork'
+    ]))
+
+    sys_cnt = {
+    'read' : 0,
+    'trace' : 0,
+    'exec' : 0,
+    'open' : 0,
+    'close' : 0,
+    'fork' : 0,
+    }
+
+    sys_cnt['fork'] += 1
+    s = r'3: syscall fork\(trace counts: ' + str(sys_cnt['fork']) + r'\) -> 4'
+    r.match(s)
+    
+    s = r'^5: syscall fork\(trace counts: \d+\) -> \d+'
+    r.match(s)
+    
+    s = r'^6: syscall fork\(trace counts: \d+\) -> \d+'
+    r.match(s)
+
+    s = r'^\d+: syscall fork\(trace counts: \d+\) -> -1'
+    r.match(s)
+    
+    r.match('^ALL TESTS PASSED')
+
+@test(14, "sysinfotest")
+def test_sysinfotest():
+    r.run_qemu(shell_script([
+        'sysinfotest'
+    ]))
+    r.match('^sysinfotest: OK', no=[".* FAIL .*"])
+
+@test(1, "time")
+def test_time():
+    check_time()
+
+run_tests()
+
diff --git a/grade-lab-util b/grade-lab-util
deleted file mode 100755
index 9032ea6..0000000
--- a/grade-lab-util
+++ /dev/null
@@ -1,86 +0,0 @@
-#!/usr/bin/env python3
-
-import re
-from gradelib import *
-
-r = Runner(save("xv6.out"))
-
-@test(5, "sleep, no arguments")
-def test_sleep_no_args():
-    r.run_qemu(shell_script([
-        'sleep'
-    ]))
-    r.match(no=["exec .* failed", "$ sleep\n$"])
-
-@test(5, "sleep, returns")
-def test_sleep_no_args():
-    r.run_qemu(shell_script([
-        'sleep',
-        'echo OK'
-    ]))
-    r.match('^OK$', no=["exec .* failed", "$ sleep\n$"])
-
-@test(10, "sleep, makes syscall")
-def test_sleep():
-    r.run_qemu(shell_script([
-        'sleep 10',
-        'echo FAIL'
-    ]), stop_breakpoint('sys_sleep'))
-    r.match('\\$ sleep 10', no=['FAIL'])
-
-@test(20, "pingpong")
-def test_pingpong():
-    r.run_qemu(shell_script([
-        'pingpong', 'echo OK'
-    ]))
-    r.match('^\\d+: received ping$', '^\\d+: received pong$', '^OK$')
-
-@test(20, "primes")
-def test_primes():
-    r.run_qemu(shell_script([
-        'primes', 'echo OK'
-    ]))
-    args = ['prime %d' % i for i in [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31]]
-    args.append('^OK$')
-    r.match(*args)
-
-@test(10, "find, in current directory")
-def test_find_curdir():
-    fn = random_str()
-    r.run_qemu(shell_script([
-        'echo > %s' % fn,
-        'find . %s' % fn
-    ]))
-    r.match('./%s' % fn)
-
-@test(10, "find, recursive")
-def test_find_recursive():
-    needle = random_str()
-    dirs = [random_str() for _ in range(3)]
-    r.run_qemu(shell_script([
-        'mkdir %s' % dirs[0],
-        'echo > %s/%s' % (dirs[0], needle),
-        'mkdir %s/%s' % (dirs[0], dirs[1]),
-        'echo > %s/%s/%s' % (dirs[0], dirs[1], needle),
-        'mkdir %s' % dirs[2],
-        'echo > %s/%s' % (dirs[2], needle),
-        'find . %s' % needle
-    ]))
-    r.match('./%s/%s' % (dirs[0], needle),
-            './%s/%s/%s' % (dirs[0], dirs[1], needle),
-            './%s/%s' % (dirs[2], needle))
-
-@test(19, "xargs")
-def test_xargs():
-    r.run_qemu(shell_script([
-        'sh < xargstest.sh',
-        'echo DONE',
-    ], 'DONE'))
-    matches = re.findall("hello", r.qemu.output)
-    assert_equal(len(matches), 3, "Number of appearances of 'hello'")
-
-@test(1, "time")
-def test_time():
-    check_time()
-    
-run_tests()
diff --git a/kernel/proc.c b/kernel/proc.c
index 58a8a0b..a343244 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -310,6 +310,8 @@ fork(void)
 
   safestrcpy(np->name, p->name, sizeof(p->name));
 
+  // 复制掩码
+  np->tracemask = p->tracemask;
   pid = np->pid;
 
   release(&np->lock);
diff --git a/kernel/proc.h b/kernel/proc.h
index d021857..7eabad0 100644
--- a/kernel/proc.h
+++ b/kernel/proc.h
@@ -91,6 +91,7 @@ struct proc {
   int killed;                  // If non-zero, have been killed
   int xstate;                  // Exit status to be returned to parent's wait
   int pid;                     // Process ID
+  int tracemask;               // Trace Mask
 
   // wait_lock must be held when using this:
   struct proc *parent;         // Parent process
diff --git a/kernel/syscall.c b/kernel/syscall.c
index ed65409..3c81e5f 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -7,6 +7,11 @@
 #include "syscall.h"
 #include "defs.h"
 
+// 保留系统调用别名
+char* syscalls_name[24] = {"", "fork", "exit", "wait", "pipe", "read", "kill", "exec",
+                      "fstat", "chdir", "dup", "getpid", "sbrk", "sleep", "uptime",
+                      "open", "write", "mknod", "unlink", "link", "mkdir", "close", "trace"};
+
 // Fetch the uint64 at addr from the current process.
 int
 fetchaddr(uint64 addr, uint64 *ip)
@@ -101,6 +106,7 @@ extern uint64 sys_unlink(void);
 extern uint64 sys_link(void);
 extern uint64 sys_mkdir(void);
 extern uint64 sys_close(void);
+extern uint64 sys_trace(void);
 
 // An array mapping syscall numbers from syscall.h
 // to the function that handles the system call.
@@ -126,6 +132,7 @@ static uint64 (*syscalls[])(void) = {
 [SYS_link]    sys_link,
 [SYS_mkdir]   sys_mkdir,
 [SYS_close]   sys_close,
+[SYS_trace]   sys_trace,
 };
 
 void
@@ -139,6 +146,9 @@ syscall(void)
     // Use num to lookup the system call function for num, call it,
     // and store its return value in p->trapframe->a0
     p->trapframe->a0 = syscalls[num]();
+    if (p->tracemask & (1 << num)) {
+       printf("%d: syscall %s -> %d\n",p->pid, syscalls_name[num], p->trapframe->a0);
+    }
   } else {
     printf("%d %s: unknown sys call %d\n",
             p->pid, p->name, num);
diff --git a/kernel/syscall.h b/kernel/syscall.h
index bc5f356..cc112b9 100644
--- a/kernel/syscall.h
+++ b/kernel/syscall.h
@@ -20,3 +20,4 @@
 #define SYS_link   19
 #define SYS_mkdir  20
 #define SYS_close  21
+#define SYS_trace  22
diff --git a/kernel/sysproc.c b/kernel/sysproc.c
index 3b4d5bd..46af86b 100644
--- a/kernel/sysproc.c
+++ b/kernel/sysproc.c
@@ -91,3 +91,13 @@ sys_uptime(void)
   release(&tickslock);
   return xticks;
 }
+
+uint64
+sys_trace(void)
+{
+  int n;
+  argint(0, &n);
+  if(n<0) return -1;
+  myproc()->tracemask = n;
+  return 0;
+}
diff --git a/user/trace.c b/user/trace.c
new file mode 100644
index 0000000..386bfc1
--- /dev/null
+++ b/user/trace.c
@@ -0,0 +1,29 @@
+#include "kernel/param.h"
+#include "kernel/types.h"
+#include "kernel/stat.h"
+#include "user/user.h"
+int
+main(int argc, char *argv[])
+{
+  int i;
+  //存储待跟踪程序的名称和参数
+  char *nargv[MAXARG];
+
+  //保证trace的参数不少于三个，并且跟踪的系统调用号在0-99之间
+  if(argc < 3 || (argv[1][0] < '0' || argv[1][0] > '9')){
+    fprintf(2, "Usage: %s mask command\n", argv[0]);
+    exit(1);
+  }
+  //调用trace系统调用，传入待跟踪系统调用号
+  if (trace(atoi(argv[1])) < 0) {
+    fprintf(2, "%s: trace failed\n", argv[0]);
+    exit(1);
+  }
+  //保存待跟踪程序的名称和参数
+  for(i = 2; i < argc && i < MAXARG; i++){
+    nargv[i-2] = argv[i];
+  }
+  //运行待跟踪的程序
+  exec(nargv[0], nargv);
+  exit(0);
+}
diff --git a/user/user.h b/user/user.h
index 075769d..36603a0 100644
--- a/user/user.h
+++ b/user/user.h
@@ -23,6 +23,7 @@ int getpid(void);
 char *sbrk(int);
 int sleep(int);
 int uptime(void);
+int trace(int);
 
 // ulib.c
 int stat(const char *, struct stat *);
diff --git a/user/usys.pl b/user/usys.pl
index 01e426e..9c97b05 100755
--- a/user/usys.pl
+++ b/user/usys.pl
@@ -36,3 +36,4 @@ entry("getpid");
 entry("sbrk");
 entry("sleep");
 entry("uptime");
+entry("trace");