Implement the write system call, w/ E

src/userprog/syscall.c

@@ -29,7 +29,7 @@ static void syscall_seek (int fd, unsigned position);
 static unsigned syscall_tell (int fd);
 static void syscall_close (int fd);
 
-static void *validate_user_pointer (void *ptr, size_t size);
+static void *validate_user_pointer (const void *ptr, size_t size);
 
 /* A struct defining a syscall_function pointer along with its arity. */
 typedef struct
@@ -157,10 +157,26 @@ syscall_read (int fd UNUSED, void *buffer UNUSED, unsigned size UNUSED)
 }
 
 static int
-syscall_write (int fd UNUSED, const void *buffer UNUSED, unsigned size UNUSED)
+syscall_write (int fd, const void *buffer, unsigned size)
 {
-  //TODO
-  return 0;
+  /* Only console (fd = 1) or other files, not including STDIN, (fd > 1) are
+     allowed. */
+  if (fd <= 0)
+    return 0;
+
+  validate_user_pointer (buffer, size);
+
+  if (fd == STDOUT_FILENO)
+    {
+      /* Writing to the console. */
+      putbuf (buffer, size);
+      return size;
+    }
+  else
+    {
+      /* Writing to a file. */
+      return 0; // TODO: Implement Write to Files
+    }
 }
 
 static void
@@ -187,7 +203,7 @@ syscall_close (int fd UNUSED)
    thread_exit) if the memory is invalid. Otherwise, returns the PTR given.
    If the size is 0, the function does no checks and returns PTR.*/
 static void *
-validate_user_pointer (void *ptr, size_t size)
+validate_user_pointer (const void *ptr, size_t size)
 {
   if (size > 0 && (ptr == NULL ||
                    !is_user_vaddr (ptr) ||