Understanding Linux Network Internals

Data Structures Featured in This Part of the Book

The section "Important Data Structures" in Chapter 16 provided a brief overview of the data structures used by the bridging code. This section provides a field-by-field description of them. The trivial ones, such as mac_addr and br_config_bpdu, do not need dedicated sections.

bridge_id Structure

We saw in the section "Bridge and Port IDs" in Chapter 15 that bridge IDs have two components, the priority and the address:

unsigned char prio[2]

Bridge priority

unsigned char addr[6]

Bridge MAC address

Note that the data structure definition does not reflect the changes introduced by 802.1t.

net_bridge_fdb_entry Structure

These are the fields that are used to define each entry in the forwarding database:

struct hlist_node list

Pointer used to link the data structure into the bucket's list of colliding elements.

struct net_bridge_port *dst

Bridge port.

struct rcu_head rcu

Used when removing the data structure using the read-copy-update (RCU) scheme (see br_fdb_put in net/bridge/br_fdb.c).

atomic_t use_count

Reference count. See the section "Lookups" in Chapter 30.

unsigned long ageing_timer

Aging timer. Different parts of the kernel spell this as aging or ageing. See the section "Aging" in Chapter 16.

mac_addr addr

MAC address. This is the key field used by the lookup routines.

unsigned char is_local

When this flag is 1, the MAC address addr is configured on a local device.

unsigned char is_static

When this flag is 1, the MAC address addr is ...