[Xcb] [PATCH] XCB-XML: Proposal for alignment padding

[Evgeny M. Zubok]

Below an example of request with a group of not aligned
lists. randrproto.txt describes an encoding of RRSetCrtcGamme as:

    RRSetCrtcGamma
	1	CARD8			major opcode
	1	24			RandR opcode
	2	3+(6n+2)/4		length
	4	CRTC			crtc
	2	n			size
	2				unused
	2n	LISTofCARD16		red
	2n	LISTofCARD16		green
	2n	LISTofCARD16		blue
	p				unused, p=pad(6n)


The specification states that there is no alignments between
lists. However, c_client.py generates the implementation of
xcb_randr_set_crtc_gamma(_checked) with alignments. Is there a bug here?
The following is the exerpt from randr.c:

    xcb_parts[2].iov_base = (char *) &xcb_out;
    xcb_parts[2].iov_len = sizeof(xcb_out);
    xcb_parts[3].iov_base = 0;
    xcb_parts[3].iov_len = -xcb_parts[2].iov_len & 3;
    xcb_parts[4].iov_base = (char *) red;
    xcb_parts[4].iov_len = size * sizeof(uint16_t);
    xcb_parts[5].iov_base = 0;
    xcb_parts[5].iov_len = -xcb_parts[4].iov_len & 3;
    xcb_parts[6].iov_base = (char *) green;
    xcb_parts[6].iov_len = size * sizeof(uint16_t);
    xcb_parts[7].iov_base = 0;
    xcb_parts[7].iov_len = -xcb_parts[6].iov_len & 3;
    xcb_parts[8].iov_base = (char *) blue;
    xcb_parts[8].iov_len = size * sizeof(uint16_t);
    xcb_parts[9].iov_base = 0;
    xcb_parts[9].iov_len = -xcb_parts[8].iov_len & 3;
    xcb_ret.sequence = xcb_send_request(c, XCB_REQUEST_CHECKED, xcb_parts + 2, &xcb_req);
    return xcb_ret;


My patch has XML description without padding between lists and with
pad (with an optional expression) at the bottom of structure:

	<request name="SetCrtcGamma" opcode="24">
		<field type="CRTC" name="crtc" />
		<field type="CARD16" name="size" />
		<pad bytes="2"/>
		<list type="CARD16" name="red">
			<fieldref>size</fieldref>
		</list>
		<list type="CARD16" name="green">
			<fieldref>size</fieldref>
		</list>
		<list type="CARD16" name="blue">
			<fieldref>size</fieldref>
		</list>
		<pad align="4">
		  <op op="*">
		    <fieldref>size</fieldref>
		    <value>6</value>
		  </op>
		</pad>
	</request>

The improved code generator actually should generate

    xcb_parts[2].iov_base = (char *) &xcb_out;
    xcb_parts[2].iov_len = sizeof(xcb_out);
    xcb_parts[3].iov_base = (char *) red;
    xcb_parts[3].iov_len = size * sizeof(uint16_t);
    xcb_parts[4].iov_base = (char *) green;
    xcb_parts[4].iov_len = size * sizeof(uint16_t);
    xcb_parts[5].iov_base = (char *) blue;
    xcb_parts[5].iov_len = size * sizeof(uint16_t);
    xcb_parts[6].iov_base = 0;
    xcb_parts[6].iov_len = -(size * 6) & 3;
    xcb_ret.sequence = xcb_send_request(c, XCB_REQUEST_CHECKED, xcb_parts + 2, &xcb_req);
    return xcb_ret;