Speed up buffer resetting (#10)

The combination of kmalloc and memset can be replaced with
kzalloc, resulting in faster execution.

Reference results:
- kzalloc: 120 ns
- kmalloc: 350 ns, memset: 500 ns

Author: YiChianLin

http_server.c

@@ -159,7 +159,7 @@ static int http_server_worker(void *arg)
     allow_signal(SIGKILL);
     allow_signal(SIGTERM);
 
-    buf = kmalloc(RECV_BUFFER_SIZE, GFP_KERNEL);
+    buf = kzalloc(RECV_BUFFER_SIZE, GFP_KERNEL);
     if (!buf) {
         pr_err("can't allocate memory!\n");
         return -1;
@@ -169,9 +169,7 @@ static int http_server_worker(void *arg)
     http_parser_init(&parser, HTTP_REQUEST);
     parser.data = &request;
     while (!kthread_should_stop()) {
-        int ret;
-        memset(buf, 0, RECV_BUFFER_SIZE);
-        ret = http_server_recv(socket, buf, RECV_BUFFER_SIZE - 1);
+        int ret = http_server_recv(socket, buf, RECV_BUFFER_SIZE - 1);
         if (ret <= 0) {
             if (ret)
                 pr_err("recv error: %d\n", ret);
@@ -180,6 +178,7 @@ static int http_server_worker(void *arg)
         http_parser_execute(&parser, &setting, buf, ret);
         if (request.complete && !http_should_keep_alive(&parser))
             break;
+        memset(buf, 0, RECV_BUFFER_SIZE);
     }
     kernel_sock_shutdown(socket, SHUT_RDWR);
     sock_release(socket);