Add writing to existing files and overwriting cp

src/kernel/keyboard.c

@@ -51,12 +51,12 @@ static void append_sequence(const char *s) {
   }
 }
 
-static uint64_t stream_write(__attribute__((unused)) const stream_t *self, __attribute__((unused)) const char *from,
+static uint64_t stream_write(__attribute__((unused)) stream_t *self, __attribute__((unused)) const char *from,
                              __attribute__((unused)) uint64_t bytes) {
   return 0;
 }
 
-static uint64_t stream_read(__attribute__((unused)) const stream_t *self, uint64_t max, char *to) {
+static uint64_t stream_read(__attribute__((unused)) stream_t *self, uint64_t max, char *to) {
   while (!buffer_length) {
     __asm__ volatile("sti");
     process_next();
@@ -79,10 +79,14 @@ static uint64_t stream_read(__attribute__((unused)) const stream_t *self, uint64
   return size;
 }
 
+static uint64_t stream_truncate(__attribute__((unused)) stream_t *self, __attribute__((unused)) uint64_t size) {
+  return size;
+}
+
 static void stream_close(__attribute__((unused)) stream_t *self) {
 }
 
-static stream_t stream = {stream_write, stream_read, stream_close};
+static stream_t stream = {stream_write, stream_read, stream_truncate, stream_close};
 
 static void on_key(uint8_t scancode) {
   const uint8_t pressed = !(scancode & 0x80);