[B.A.T.M.A.N.] [PATCHv4 02/13] batman-adv: use vid when computing local and global TT CRC

Antonio Quartulli
2013-06-04T10:11:40Z

now that each TT entry is characterised by a VLAN ID, the
latter has to be taken into consideration when computing the
local/global table CRC as it would be theoretically possible
to have the same client in two different VLANs

Signed-off-by: Antonio Quartulli <antonio@open-mesh.com>
---
translation-table.c | 35 +++++++++++++++++++++++++++++++----
1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/translation-table.c b/translation-table.c
index 708bafe..0427d2f 100644
--- a/translation-table.c
+++ b/translation-table.c
@@ -1506,6 +1506,24 @@ out:
* batadv_tt_global_crc - calculates the checksum of the local table belonging
* to the given orig_node
* @bat_priv: the bat priv with all the soft interface information
+ * @orig_node: originator for which the CRC should be computed
+ *
+ * This function computes the checksum for the global table corresponding to a
+ * particular originator. In particular the checksum is computed as follows: for
+ * each client connected to the originator the CRC32C of the MAC address and the
+ * VID is computed and then all the CRC32Cs of the various clients are xor'ed
+ * together.
+ *
+ * The idea behind is that CRC32C should be used as much as possible in order to
+ * produce a unique hash of the table, but since the order which is used to feed
+ * the CRC32C function affects the result and since every node in the network
+ * probably sorts the clients differently, the hash function cannot be directly
+ * computed over the entire table. Hence the CRC32C is used only on
+ * the single client entry, while all the results are then xor'ed together
+ * because the XOR operation can combine them all while trying to reduce the
+ * noise as much as possible.
+ *
+ * Returns the checksum of the global table of a given originator
*/
static uint32_t batadv_tt_global_crc(struct batadv_priv *bat_priv,
struct batadv_orig_node *orig_node)
@@ -1514,7 +1532,7 @@ static uint32_t batadv_tt_global_crc(struct batadv_priv *bat_priv,
struct batadv_tt_common_entry *tt_common;
struct batadv_tt_global_entry *tt_global;
struct hlist_head *head;
- uint32_t i, crc = 0;
+ uint32_t i, crc_tmp, crc = 0;

for (i = 0; i < hash->size; i++) {
head = &hash->table[i];
@@ -1545,7 +1563,9 @@ static uint32_t batadv_tt_global_crc(struct batadv_priv *bat_priv,
orig_node))
continue;

- crc ^= crc32c(0, tt_common->addr, ETH_ALEN);
+ crc_tmp = crc32c(0, &tt_common->vid,
+ sizeof(tt_common->vid));
+ crc ^= crc32c(crc_tmp, tt_common->addr, ETH_ALEN);
}
rcu_read_unlock();
}
@@ -1556,13 +1576,18 @@ static uint32_t batadv_tt_global_crc(struct batadv_priv *bat_priv,
/**
* batadv_tt_local_crc - calculates the checksum of the local table
* @bat_priv: the bat priv with all the soft interface information
+ *
+ * For details about the computation, please refer to the documentation for
+ * batadv_tt_global_crc().
+ *
+ * Returns the checksum of the local table
*/
static uint32_t batadv_tt_local_crc(struct batadv_priv *bat_priv)
{
struct batadv_hashtable *hash = bat_priv->tt.local_hash;
struct batadv_tt_common_entry *tt_common;
struct hlist_head *head;
- uint32_t i, crc = 0;
+ uint32_t i, crc_tmp, crc = 0;

for (i = 0; i < hash->size; i++) {
head = &hash->table[i];
@@ -1575,7 +1600,9 @@ static uint32_t batadv_tt_local_crc(struct batadv_priv *bat_priv)
if (tt_common->flags & BATADV_TT_CLIENT_NEW)
continue;

- crc ^= crc32c(0, tt_common->addr, ETH_ALEN);
+ crc_tmp = crc32c(0, &tt_common->vid,
+ sizeof(tt_common->vid));
+ crc ^= crc32c(crc_tmp, tt_common->addr, ETH_ALEN);
}
rcu_read_unlock();
}
--
1.8.1.5