source: bootcd/isolinux/syslinux-6.03/gpxe/src/net/iobpad.c

/*
 * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

FILE_LICENCE ( GPL2_OR_LATER );

/**
 * @file
 *
 * I/O buffer padding
 *
 */

#include <string.h>
#include <gpxe/iobuf.h>

/**
 * Pad I/O buffer
 *
 * @v iobuf             I/O buffer
 * @v min_len           Minimum length
 *
 * This function pads and aligns I/O buffers, for devices that
 * aren't capable of padding in hardware, or that require specific
 * alignment in TX buffers.  The packet data will end up aligned to a
 * multiple of @c IOB_ALIGN.
 *
 * @c min_len must not exceed @v IOB_ZLEN.
 */
void iob_pad ( struct io_buffer *iobuf, size_t min_len ) {
        void *data;
        size_t len;
        size_t headroom;
        signed int pad_len;

        assert ( min_len <= IOB_ZLEN );

        /* Move packet data to start of I/O buffer.  This will both
         * align the data (since I/O buffers are aligned to
         * IOB_ALIGN) and give us sufficient space for the
         * zero-padding
         */
        data = iobuf->data;
        len = iob_len ( iobuf );
        headroom = iob_headroom ( iobuf );
        iob_push ( iobuf, headroom );
        memmove ( iobuf->data, data, len );
        iob_unput ( iobuf, headroom );

        /* Pad to minimum packet length */
        pad_len = ( min_len - iob_len ( iobuf ) );
        if ( pad_len > 0 )
                memset ( iob_put ( iobuf, pad_len ), 0, pad_len );
}