+ bool continue_on_write_error = 0;
+#if CONFIG_FEATURE_COPYBUF_KB <= 4
+ char buffer[CONFIG_FEATURE_COPYBUF_KB * 1024];
+ enum { buffer_size = sizeof(buffer) };
+#else
+ char *buffer;
+ int buffer_size;
+#endif
+
+ if (size < 0) {
+ size = -size;
+ continue_on_write_error = 1;
+ }
+
+#if CONFIG_FEATURE_COPYBUF_KB > 4
+ if (size > 0 && size <= 4 * 1024)
+ goto use_small_buf;
+ /* We want page-aligned buffer, just in case kernel is clever
+ * and can do page-aligned io more efficiently */
+ buffer = mmap(NULL, CONFIG_FEATURE_COPYBUF_KB * 1024,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANON,
+ /* ignored: */ -1, 0);
+ buffer_size = CONFIG_FEATURE_COPYBUF_KB * 1024;
+ if (buffer == MAP_FAILED) {
+ use_small_buf:
+ buffer = alloca(4 * 1024);
+ buffer_size = 4 * 1024;
+ }
+#endif