app: Use C FILE instead of POSIX fd, and switch back to /etc/motd

apps/app.c

@@ -15,23 +15,20 @@ int main()
     atexit(bye);
     printf("Welcome to %s from userspace (pid %d)!\n", "Luna", getpid());
 
-    mkdir("/home", 0755);
-    mkdir("/home/user", 0755);
-
-    int fd = open("/home/user/notes.txt", O_RDWR | O_CREAT, 0644);
-    if (fd < 0)
+    FILE* f = fopen("/etc/motd", "r");
+    if (!f)
     {
-        perror("open");
+        perror("fopen");
         return 1;
     }
 
     char buffer[512];
-    ssize_t nread = read(fd, buffer, sizeof(buffer));
+    size_t nread = fread(buffer, 1, sizeof(buffer), f);
     buffer[nread] = 0;
 
-    printf("/home/user/notes.txt says: %s", buffer);
+    printf("/etc/motd says: %s", buffer);
 
-    close(fd);
+    fclose(f);
 
     time_t now = time(NULL);
     printf("date: %s", ctime(&now));