net/checksum.c

   1 /*
   2  *  IP checksumming functions.
   3  *  (c) 2008 Gerd Hoffmann <kraxel@redhat.com>
   4  *
   5  *  This program is free software; you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation; under version 2 or later of the License.
   8  *
   9  *  This program is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  *  GNU 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, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 #include "qemu-common.h"
  19 #include "net/checksum.h"
  20
  21 #define PROTO_TCP  6
  22 #define PROTO_UDP 17
  23
  24 uint32_t net_checksum_add_cont(int len, uint8_t *buf, int seq)
  25 {
  26     uint32_t sum = 0;
  27     int i;
  28
  29     for (i = seq; i < seq + len; i++) {
  30         if (i & 1) {
  31             sum += (uint32_t)buf[i - seq];
  32         } else {
  33             sum += (uint32_t)buf[i - seq] << 8;
  34         }
  35     }
  36     return sum;
  37 }
  38
  39 uint16_t net_checksum_finish(uint32_t sum)
  40 {
  41     while (sum>>16)
  42         sum = (sum & 0xFFFF)+(sum >> 16);
  43     return ~sum;
  44 }
  45
  46 uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto,
  47                              uint8_t *addrs, uint8_t *buf)
  48 {
  49     uint32_t sum = 0;
  50
  51     sum += net_checksum_add(length, buf);         // payload
  52     sum += net_checksum_add(8, addrs);            // src + dst address
  53     sum += proto + length;                        // protocol & length
  54     return net_checksum_finish(sum);
  55 }
  56
  57 void net_checksum_calculate(uint8_t *data, int length)
  58 {
  59     int hlen, plen, proto, csum_offset;
  60     uint16_t csum;
  61
  62     if ((data[14] & 0xf0) != 0x40)
  63         return; /* not IPv4 */
  64     hlen  = (data[14] & 0x0f) * 4;
  65     plen  = (data[16] << 8 | data[17]) - hlen;
  66     proto = data[23];
  67
  68     switch (proto) {
  69     case PROTO_TCP:
  70         csum_offset = 16;
  71         break;
  72     case PROTO_UDP:
  73         csum_offset = 6;
  74         break;
  75     default:
  76         return;
  77     }
  78
  79     if (plen < csum_offset+2)
  80         return;
  81
  82     data[14+hlen+csum_offset]   = 0;
  83     data[14+hlen+csum_offset+1] = 0;
  84     csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen);
  85     data[14+hlen+csum_offset]   = csum >> 8;
  86     data[14+hlen+csum_offset+1] = csum & 0xff;
  87 }
  88
  89 uint32_t
  90 net_checksum_add_iov(const struct iovec *iov, const unsigned int iov_cnt,
  91                      uint32_t iov_off, uint32_t size)
  92 {
  93     size_t iovec_off, buf_off;
  94     unsigned int i;
  95     uint32_t res = 0;
  96     uint32_t seq = 0;
  97
  98     iovec_off = 0;
  99     buf_off = 0;
 100     for (i = 0; i < iov_cnt && size; i++) {
 101         if (iov_off < (iovec_off + iov[i].iov_len)) {
 102             size_t len = MIN((iovec_off + iov[i].iov_len) - iov_off , size);
 103             void *chunk_buf = iov[i].iov_base + (iov_off - iovec_off);
 104
 105             res += net_checksum_add_cont(len, chunk_buf, seq);
 106             seq += len;
 107
 108             buf_off += len;
 109             iov_off += len;
 110             size -= len;
 111         }
 112         iovec_off += iov[i].iov_len;
 113     }
 114     return res;
 115 }