Factor out code for composing benign packets.

The bonding code in vswitch sends out gratuitous learning packets that
are supposed to teach switches but not cause anything else to happen on
the network.  Some upcoming code wants to synthesize packets with similar
properties, so factor this code into a new function so that it can be
used in both places.

1 files changed, 58 insertions, 0 deletions

diff --git a/lib/packets.c b/lib/packets.c
new file mode 100644
index 00000000..0547791a
--- /dev/null
+++ b/lib/packets.c
@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2009 Nicira Networks.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+#include "packets.h"
+#include <netinet/in.h>
+#include "ofpbuf.h"
+
+/* Fills 'b' with an 802.2 SNAP packet with Ethernet source address 'eth_src',
+ * the Nicira OUI as SNAP organization and 'snap_type' as SNAP type.  The text
+ * string in 'tag' is enclosed as the packet payload.
+ *
+ * This function is used by Open vSwitch to compose packets in cases where
+ * context is important but content doesn't (or shouldn't) matter.  For this
+ * purpose, 'snap_type' should be a random number and 'tag' should be an
+ * English phrase that explains the purpose of the packet.  (The English phrase
+ * gives hapless admins running Wireshark the opportunity to figure out what's
+ * going on.) */
+void
+compose_benign_packet(struct ofpbuf *b, const char *tag, uint16_t snap_type,
+                      const uint8_t eth_src[ETH_ADDR_LEN])
+{
+    struct eth_header *eth;
+    struct llc_snap_header *llc_snap;
+
+    /* Compose basic packet structure.  (We need the payload size to stick into
+     * the 802.2 header.) */
+    ofpbuf_clear(b);
+    eth = ofpbuf_put_zeros(b, ETH_HEADER_LEN);
+    llc_snap = ofpbuf_put_zeros(b, LLC_SNAP_HEADER_LEN);
+    ofpbuf_put(b, tag, strlen(tag) + 1); /* Includes null byte. */
+    ofpbuf_put(b, eth_src, ETH_ADDR_LEN);
+
+    /* Compose 802.2 header. */
+    memcpy(eth->eth_dst, eth_addr_broadcast, ETH_ADDR_LEN);
+    memcpy(eth->eth_src, eth_src, ETH_ADDR_LEN);
+    eth->eth_type = htons(b->size - ETH_HEADER_LEN);
+
+    /* Compose LLC, SNAP headers. */
+    llc_snap->llc.llc_dsap = LLC_DSAP_SNAP;
+    llc_snap->llc.llc_ssap = LLC_SSAP_SNAP;
+    llc_snap->llc.llc_cntl = LLC_CNTL_SNAP;
+    memcpy(llc_snap->snap.snap_org, "\x00\x23\x20", 3);
+    llc_snap->snap.snap_type = htons(snap_type);
+}