gpxe/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., 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18
  19 FILE_LICENCE ( GPL2_OR_LATER );
  20
  21 /**
  22  * @file
  23  *
  24  * I/O buffer padding
  25  *
  26  */
  27
  28 #include <string.h>
  29 #include <gpxe/iobuf.h>
  30
  31 /**
  32  * Pad I/O buffer
  33  *
  34  * @v iobuf             I/O buffer
  35  * @v min_len           Minimum length
  36  *
  37  * This function pads and aligns I/O buffers, for devices that
  38  * aren't capable of padding in hardware, or that require specific
  39  * alignment in TX buffers.  The packet data will end up aligned to a
  40  * multiple of @c IOB_ALIGN.
  41  *
  42  * @c min_len must not exceed @v IOB_ZLEN.
  43  */
  44 void iob_pad ( struct io_buffer *iobuf, size_t min_len ) {
  45         void *data;
  46         size_t len;
  47         size_t headroom;
  48         signed int pad_len;
  49
  50         assert ( min_len <= IOB_ZLEN );
  51
  52         /* Move packet data to start of I/O buffer.  This will both
  53          * align the data (since I/O buffers are aligned to
  54          * IOB_ALIGN) and give us sufficient space for the
  55          * zero-padding
  56          */
  57         data = iobuf->data;
  58         len = iob_len ( iobuf );
  59         headroom = iob_headroom ( iobuf );
  60         iob_push ( iobuf, headroom );
  61         memmove ( iobuf->data, data, len );
  62         iob_unput ( iobuf, headroom );
  63
  64         /* Pad to minimum packet length */
  65         pad_len = ( min_len - iob_len ( iobuf ) );
  66         if ( pad_len > 0 )
  67                 memset ( iob_put ( iobuf, pad_len ), 0, pad_len );
  68 }