Understanding Linux Network Internals

Data Structures Featured in This Part of the Book

The section "Main Data Structures" in Chapter 32 gave a brief overview of the main data structures, and Figure 34-1 in Chapter 34 can help you understand the relationships between them. This section provides a detailed description of each data structure type. Figure 36-5 shows the file that defines each data structure.

Figure 36-5. Distribution of data structures in kernel files

fib_table Structure

A fib_table structure is created for each routing table instance. The structure consists mainly of a routing table identifier and a set of function pointers used to manage the table:

unsigned char tb_id

Routing table identifier. In include/linux/rtnetlink.h, you can find the rt_class_t list of predefined values, such as RT_TABLE_LOCAL.

unsigned tb_stamp

Not used.

int (*tb_lookup)(struct fib_table *tb, const struct flowi *flp, struct fib_result *res)

The function called by the fib_lookup routine described in Chapter 35.

int (*tb_insert)(struct fib_table *table, struct rtmsg *r,struct kern_rta *rta, struct nlmsghdr *n, struct netlink_skb_parms *req)

int (*tb_delete)(struct fib_table *table, struct rtmsg *r, struct kern_rta *rta, struct nlmsghdr *n, struct netlink_skb_parms *req);

tb_insert is called by inet_rtm_newroute and ip_rt_ioctl to process the ip route add/change/replace/prepend/append/test and route add user-space commands. Similarly, ...