[zbin] Fix check for existence of most recent output byte
[ipxe.git] / src / net / iobpad.c
1 /*
2 * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License as
6 * published by the Free Software Foundation; either version 2 of the
7 * License, or any later version.
8 *
9 * This program is distributed in the hope that it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
17 * 02110-1301, USA.
18 */
19
20 FILE_LICENCE ( GPL2_OR_LATER );
21
22 /**
23 * @file
24 *
25 * I/O buffer padding
26 *
27 */
28
29 #include <string.h>
30 #include <ipxe/iobuf.h>
31
32 /**
33 * Pad I/O buffer
34 *
35 * @v iobuf I/O buffer
36 * @v min_len Minimum length
37 *
38 * This function pads and aligns I/O buffers, for devices that
39 * aren't capable of padding in hardware, or that require specific
40 * alignment in TX buffers. The packet data will end up aligned to a
41 * multiple of @c IOB_ALIGN.
42 *
43 * @c min_len must not exceed @v IOB_ZLEN.
44 */
45 void iob_pad ( struct io_buffer *iobuf, size_t min_len ) {
46 void *data;
47 size_t len;
48 size_t headroom;
49 signed int pad_len;
50
51 assert ( min_len <= IOB_ZLEN );
52
53 /* Move packet data to start of I/O buffer. This will both
54 * align the data (since I/O buffers are aligned to
55 * IOB_ALIGN) and give us sufficient space for the
56 * zero-padding
57 */
58 data = iobuf->data;
59 len = iob_len ( iobuf );
60 headroom = iob_headroom ( iobuf );
61 iob_push ( iobuf, headroom );
62 memmove ( iobuf->data, data, len );
63 iob_unput ( iobuf, headroom );
64
65 /* Pad to minimum packet length */
66 pad_len = ( min_len - iob_len ( iobuf ) );
67 if ( pad_len > 0 )
68 memset ( iob_put ( iobuf, pad_len ), 0, pad_len );
69 }