在策略路由之初始化中有介紹過,每個協議族要支持策略路由,需要向策略路由框架註冊一個struct fib_rules_ops對象,對於AF_INET協議族,該對象是fib_rules_net_ops,該對象的核心是一組回調函數,這篇筆記就來具體分析下AF_INET協議族的這些核心回調函數的實現。
源代碼路徑 | 說明 |
---|---|
net/core/fib_rules.c | 策略路由非協議相關實現 |
net/ipv4/fib_rules.c | 策略路由的IPv4實現 |
include/net/fib_rules.h | 策略路由相關數據結構定義 |
1. fib_rules_ops對象
static struct fib_rules_ops fib4_rules_ops_template = {
.family = AF_INET,
.rule_size = sizeof(struct fib4_rule),
.addr_size = sizeof(u32),
.action = fib4_rule_action,
.match = fib4_rule_match,
.configure = fib4_rule_configure,
.compare = fib4_rule_compare,
.fill = fib4_rule_fill,
.default_pref = fib4_rule_default_pref,
.nlmsg_payload = fib4_rule_nlmsg_payload,
.flush_cache = fib4_rule_flush_cache,
.nlgroup = RTNLGRP_IPV4_RULE,
.policy = fib4_rule_policy,
.owner = THIS_MODULE,
};
2. 策略路由規則配置回調: fib4_rule_configure()
該回調在新增策略路由規則時被fib_nl_newrule()調用,它實現了AF_INET協議族相關字段的配置。
#define IPTOS_TOS_MASK 0x1E
static int fib4_rule_configure(struct fib_rule *rule, struct sk_buff *skb,
struct nlmsghdr *nlh, struct fib_rule_hdr *frh, struct nlattr **tb)
{
struct net *net = skb->sk->sk_net;
int err = -EINVAL;
struct fib4_rule *rule4 = (struct fib4_rule *) rule;
//校驗TOS,只有其中幾個bit爲1,其它必須爲0
if (frh->tos & ~IPTOS_TOS_MASK)
goto errout;
//如果action是查詢某個路由表,但是又沒有指定路由表,那麼新建一個路由表,
//指定查詢該表。這個邏輯好奇怪,爲什麼不是查詢main表或者default表呢
if (rule->table == RT_TABLE_UNSPEC) {
if (rule->action == FR_ACT_TO_TBL) {
struct fib_table *table;
table = fib_empty_table(net);
if (table == NULL) {
err = -ENOBUFS;
goto errout;
}
rule->table = table->tb_id;
}
}
//保存源IP和目的IP地址,以及掩碼
if (frh->src_len)
rule4->src = nla_get_be32(tb[FRA_SRC]);
if (frh->dst_len)
rule4->dst = nla_get_be32(tb[FRA_DST]);
rule4->src_len = frh->src_len;
rule4->srcmask = inet_make_mask(rule4->src_len);
rule4->dst_len = frh->dst_len;
rule4->dstmask = inet_make_mask(rule4->dst_len);
rule4->tos = frh->tos;
err = 0;
errout:
return err;
}
3. 比較策略路由規則是否相同: fib4_rule_compare()
static int fib4_rule_compare(struct fib_rule *rule, struct fib_rule_hdr *frh,
struct nlattr **tb)
{
struct fib4_rule *rule4 = (struct fib4_rule *) rule;
//如果比較條件中包含了地址長度,則比較地址長度
if (frh->src_len && (rule4->src_len != frh->src_len))
return 0;
if (frh->dst_len && (rule4->dst_len != frh->dst_len))
return 0;
//如果比較條件中包含了tos,則比較tos
if (frh->tos && (rule4->tos != frh->tos))
return 0;
if (frh->src_len && (rule4->src != nla_get_be32(tb[FRA_SRC])))
return 0;
if (frh->dst_len && (rule4->dst != nla_get_be32(tb[FRA_DST])))
return 0;
//返回1表示相同,0表示不同
return 1;
}
4. 比較查詢條件是否匹配策略路由規則: fib4_rule_match()
在路由查找過程中,會調用該函數檢查查詢條件(來源於數據包)和策略路由規則是否匹配,如果匹配,則執行action。
static int fib4_rule_match(struct fib_rule *rule, struct flowi *fl, int flags)
{
struct fib4_rule *r = (struct fib4_rule *) rule;
__be32 daddr = fl->fl4_dst;
__be32 saddr = fl->fl4_src;
//IP地址的比較,只關心掩碼指定的bit,只要這些bit相同,就認爲匹配
if (((saddr ^ r->src) & r->srcmask) || ((daddr ^ r->dst) & r->dstmask))
return 0;
//策略路由規則如果沒有tos(爲0),那麼無條件匹配,否則需要相等
if (r->tos && (r->tos != fl->fl4_tos))
return 0;
return 1;
}
4. 執行策略路由規則action: fib4_rule_action()
static int fib4_rule_action(struct fib_rule *rule, struct flowi *flp,
int flags, struct fib_lookup_arg *arg)
{
int err = -EAGAIN;
struct fib_table *tbl;
//根據action類型,返回不同的錯誤碼。對於FR_ACT_TO_TBL,則查詢指定路由表
switch (rule->action) {
case FR_ACT_TO_TBL:
break;
case FR_ACT_UNREACHABLE:
err = -ENETUNREACH;
goto errout;
case FR_ACT_PROHIBIT:
err = -EACCES;
goto errout;
case FR_ACT_BLACKHOLE:
default:
err = -EINVAL;
goto errout;
}
//根據路由表ID獲取路由表fib_table對象
if ((tbl = fib_get_table(rule->fr_net, rule->table)) == NULL)
goto errout;
//執行路由表的查詢回調查詢路由。返回大於0則繼續按照下一條策略路由規則查詢;
//等於0查詢成功;小於0爲查詢失敗,查詢失敗也是一種查詢成功結果,只是該結果
//屬於路由失敗而已
err = tbl->tb_lookup(tbl, flp, (struct fib_result *) arg->result);
if (err > 0)
err = -EAGAIN;
errout:
return err;
}
5. 獲取默認優先級: fib4_rule_default_pref()
添加策略路由規則時,如果沒有指定優先級,那麼如果協議族提供了該回調,那麼會調用該函數獲取一個默認的優先級。
static u32 fib4_rule_default_pref(struct fib_rules_ops *ops)
{
struct list_head *pos;
struct fib_rule *rule;
//找一個比當前最小的非零優先級小1的值作爲新增規則的優先級,即選一個除0以外,
//離已使用優先級最接近的最高優先級
if (!list_empty(&ops->rules_list)) {
pos = ops->rules_list.next;
if (pos->next != &ops->rules_list) {
rule = list_entry(pos->next, struct fib_rule, list);
if (rule->pref)
return rule->pref - 1;
}
}
return 0;
}