revise app and user lib

user/app_relativepath.c

@@ -2,6 +2,17 @@
 #include "util/string.h"
 #include "util/types.h"
 
+void pwd() {
+  char path[30];
+  read_cwd(path);
+  printu("cwd:%s\n", path);
+}
+
+void cd(const char *path) {
+  if (change_cwd(path) != 0)
+    printu("cd failed\n");
+}
+
 int main(int argc, char *argv[]) {
   int fd;
   int MAXBUF = 512;

user/user_lib.c

@@ -167,3 +167,17 @@ int unlink_u(const char *fn){
 int close(int fd) {
   return do_user_call(SYS_user_close, fd, 0, 0, 0, 0, 0, 0);
 }
+
+//
+// lib call to read present working directory (pwd)
+//
+int read_cwd(char *path) {
+  return do_user_call(SYS_user_rcwd, (uint64)path, 0, 0, 0, 0, 0, 0);
+}
+
+//
+// lib call to change pwd
+//
+int change_cwd(const char *path) {
+  return do_user_call(SYS_user_ccwd, (uint64)path, 0, 0, 0, 0, 0, 0);
+}

user/user_lib.h

@@ -33,5 +33,7 @@ int closedir_u(int fd);
 int link_u(const char *fn1, const char *fn2);
 int unlink_u(const char *fn);
 
+int read_cwd(char *path);
+int change_cwd(const char *path);
 
 #endif