unix/file: Implement MP_STREAM_FLUSH ioctl.

unix/file.c

@@ -105,7 +105,8 @@ STATIC mp_uint_t fdfile_write(mp_obj_t o_in, const void *buf, mp_uint_t size, in
 
 STATIC mp_uint_t fdfile_ioctl(mp_obj_t o_in, mp_uint_t request, uintptr_t arg, int *errcode) {
     mp_obj_fdfile_t *o = MP_OBJ_TO_PTR(o_in);
-    if (request == MP_STREAM_SEEK) {
+    switch (request) {
+        case MP_STREAM_SEEK: {
             struct mp_stream_seek_t *s = (struct mp_stream_seek_t*)arg;
             off_t off = lseek(o->fd, s->offset, s->whence);
             if (off == (off_t)-1) {
@@ -114,7 +115,14 @@ STATIC mp_uint_t fdfile_ioctl(mp_obj_t o_in, mp_uint_t request, uintptr_t arg, i
             }
             s->offset = off;
             return 0;
-    } else {
+        }
+        case MP_STREAM_FLUSH:
+            if (fsync(o->fd) < 0) {
+                *errcode = errno;
+                return MP_STREAM_ERROR;
+            }
+            return 0;
+        default:
             *errcode = EINVAL;
             return MP_STREAM_ERROR;
     }