+ static const char pad[3];
+ unsigned int i;
+ uint16_t shortlen = 0;
+ size_t longlen = 0;
+ assert(vector[0].iov_len >= 4);
+ /* set the major opcode, and the minor opcode for extensions */
+ if(req->ext)
+ {
+ const xcb_query_extension_reply_t *extension = xcb_get_extension_data(c, req->ext);
+ if(!(extension && extension->present))
+ {
+ _xcb_conn_shutdown(c);
+ return 0;
+ }
+ ((uint8_t *) vector[0].iov_base)[0] = extension->major_opcode;
+ ((uint8_t *) vector[0].iov_base)[1] = req->opcode;
+ }
+ else
+ ((uint8_t *) vector[0].iov_base)[0] = req->opcode;
+
+ /* put together the length field, possibly using BIGREQUESTS */
+ for(i = 0; i < req->count; ++i)
+ {
+ longlen += vector[i].iov_len;
+ if(!vector[i].iov_base)
+ {
+ vector[i].iov_base = (char *) pad;
+ assert(vector[i].iov_len <= sizeof(pad));
+ }
+ }
+ assert((longlen & 3) == 0);
+ longlen >>= 2;
+
+ if(longlen <= c->setup->maximum_request_length)
+ {
+ /* we don't need BIGREQUESTS. */
+ shortlen = longlen;
+ longlen = 0;
+ }
+ else if(longlen > xcb_get_maximum_request_length(c))
+ {
+ _xcb_conn_shutdown(c);