lib/packets.c

   1 /*
   2  * Copyright (c) 2009, 2010 Nicira Networks.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18 #include "packets.h"
  19 #include <netinet/in.h>
  20 #include <stdlib.h>
  21 #include "ofpbuf.h"
  22
  23 /* Parses 's' as a 16-digit hexadecimal number representing a datapath ID.  On
  24  * success stores the dpid into '*dpidp' and returns true, on failure stores 0
  25  * into '*dpidp' and returns false.
  26  *
  27  * Rejects an all-zeros dpid as invalid. */
  28 bool
  29 dpid_from_string(const char *s, uint64_t *dpidp)
  30 {
  31     *dpidp = (strlen(s) == 16 && strspn(s, "0123456789abcdefABCDEF") == 16
  32               ? strtoull(s, NULL, 16)
  33               : 0);
  34     return *dpidp != 0;
  35 }
  36
  37 bool
  38 eth_addr_from_string(const char *s, uint8_t ea[ETH_ADDR_LEN])
  39 {
  40     if (sscanf(s, ETH_ADDR_SCAN_FMT, ETH_ADDR_SCAN_ARGS(ea))
  41         == ETH_ADDR_SCAN_COUNT) {
  42         return true;
  43     } else {
  44         memset(ea, 0, ETH_ADDR_LEN);
  45         return false;
  46     }
  47 }
  48
  49 /* Fills 'b' with an 802.2 SNAP packet with Ethernet source address 'eth_src',
  50  * the Nicira OUI as SNAP organization and 'snap_type' as SNAP type.  The text
  51  * string in 'tag' is enclosed as the packet payload.
  52  *
  53  * This function is used by Open vSwitch to compose packets in cases where
  54  * context is important but content doesn't (or shouldn't) matter.  For this
  55  * purpose, 'snap_type' should be a random number and 'tag' should be an
  56  * English phrase that explains the purpose of the packet.  (The English phrase
  57  * gives hapless admins running Wireshark the opportunity to figure out what's
  58  * going on.) */
  59 void
  60 compose_benign_packet(struct ofpbuf *b, const char *tag, uint16_t snap_type,
  61                       const uint8_t eth_src[ETH_ADDR_LEN])
  62 {
  63     struct eth_header *eth;
  64     struct llc_snap_header *llc_snap;
  65
  66     /* Compose basic packet structure.  (We need the payload size to stick into
  67      * the 802.2 header.) */
  68     ofpbuf_clear(b);
  69     eth = ofpbuf_put_zeros(b, ETH_HEADER_LEN);
  70     llc_snap = ofpbuf_put_zeros(b, LLC_SNAP_HEADER_LEN);
  71     ofpbuf_put(b, tag, strlen(tag) + 1); /* Includes null byte. */
  72     ofpbuf_put(b, eth_src, ETH_ADDR_LEN);
  73
  74     /* Compose 802.2 header. */
  75     memcpy(eth->eth_dst, eth_addr_broadcast, ETH_ADDR_LEN);
  76     memcpy(eth->eth_src, eth_src, ETH_ADDR_LEN);
  77     eth->eth_type = htons(b->size - ETH_HEADER_LEN);
  78
  79     /* Compose LLC, SNAP headers. */
  80     llc_snap->llc.llc_dsap = LLC_DSAP_SNAP;
  81     llc_snap->llc.llc_ssap = LLC_SSAP_SNAP;
  82     llc_snap->llc.llc_cntl = LLC_CNTL_SNAP;
  83     memcpy(llc_snap->snap.snap_org, "\x00\x23\x20", 3);
  84     llc_snap->snap.snap_type = htons(snap_type);
  85 }