Linux内核中流量控制(17)
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7.6 tcf_proto_ops的一些相关操作

7.6.1 登记和撤销

/* Register(unregister) new classifier type */
// 登记新的tcf_proto_ops分类操作结构
int register_tcf_proto_ops(struct tcf_proto_ops *ops)
{
 struct tcf_proto_ops *t, **tp;
 int rc = -EEXIST;
 write_lock(&cls_mod_lock);
// 遍历当前tcf_proto_ops链表
 for (tp = &tcf_proto_base; (t = *tp) != NULL; tp = &t->next)
// 检查是否有名称相同的项, 有的话返回对象已存在错误
  if (!strcmp(ops->kind, t->kind))
   goto out;
// 添加到链表末尾, 也是dummy header算法
 ops->next = NULL;
 *tp = ops;
 rc = 0;
out:
 write_unlock(&cls_mod_lock);
 return rc;
}

// 撤销tcf_proto_ops分类结构
int unregister_tcf_proto_ops(struct tcf_proto_ops *ops)
{
 struct tcf_proto_ops *t, **tp;
 int rc = -ENOENT;
 write_lock(&cls_mod_lock);
// 遍历链表
 for (tp = &tcf_proto_base; (t=*tp) != NULL; tp = &t->next)
// 直接进行tcf_proto_ops结构地址比较, 相同的话中断循环
  if (t == ops)
   break;
 if (!t)
  goto out;
// 将找到的tp节点从链表中断开, 不用释放操作, 因为这些ops其实都是静态定义的
 *tp = t->next;
 rc = 0;
out:
 write_unlock(&cls_mod_lock);
 return rc;
}

7.6.2 tcf扩展

tcf扩展增加了对分类后数据进行某种操作的功能, 有点象netfilter的target，使用这些功能需要在配置内核时定义NET_CLS_ACT或NET_CLS_POLICE。

/* include/net/pkt_cls.h */
// tcf扩展结构, 如果没定义NET_CLS_ACT和NET_CLS_POLICE的话就是个空结构
struct tcf_exts
{
#ifdef CONFIG_NET_CLS_ACT
// 动作
 struct tc_action *action;
#elif defined CONFIG_NET_CLS_POLICE
// 策略
 struct tcf_police *police;
#endif
};
/* Map to export classifier specific extension TLV types to the
 * generic extensions API. Unsupported extensions must be set to 0.
 */
struct tcf_ext_map
{
 int action;
 int police;
};

/**
 * tcf_exts_is_predicative - check if a predicative extension is present
 * @exts: tc filter extensions handle
 *
 * Returns 1 if a predicative extension is present, i.e. an extension which
 * might cause further actions and thus overrule the regular tcf_result.
 */
// 返回扩展结构中的元素是否为空
static inline int
tcf_exts_is_predicative(struct tcf_exts *exts)
{
#ifdef CONFIG_NET_CLS_ACT
// !!是为了保证返回值0或1
 return !!exts->action;
#elif defined CONFIG_NET_CLS_POLICE
 return !!exts->police;
#else
 return 0;
#endif
}
/**
 * tcf_exts_is_available - check if at least one extension is present
 * @exts: tc filter extensions handle
 *
 * Returns 1 if at least one extension is present.
 */
// 实际就是cf_exts_is_predicative函数
static inline int
tcf_exts_is_available(struct tcf_exts *exts)
{
 /* All non-predicative extensions must be added here. */
 return tcf_exts_is_predicative(exts);
}
/**
 * tcf_exts_exec - execute tc filter extensions
 * @skb: socket buffer
 * @exts: tc filter extensions handle
 * @res: desired result
 *
 * Executes all configured extensions. Returns 0 on a normal execution,
 * a negative number if the filter must be considered unmatched or
 * a positive action code (TC_ACT_*) which must be returned to the
 * underlying layer.
 */
static inline int
tcf_exts_exec(struct sk_buff *skb, struct tcf_exts *exts,
        struct tcf_result *res)
{
#ifdef CONFIG_NET_CLS_ACT
 if (exts->action)
  return tcf_action_exec(skb, exts->action, res);
#elif defined CONFIG_NET_CLS_POLICE
 if (exts->police)
  return tcf_police(skb, exts->police);
#endif
 return 0;
}
 
/* net/sched/cls_api.c */
// 是否tcf扩展结构
void
tcf_exts_destroy(struct tcf_proto *tp, struct tcf_exts *exts)
{
#ifdef CONFIG_NET_CLS_ACT
 if (exts->action) {
// 释放tcf动作
  tcf_action_destroy(exts->action, TCA_ACT_UNBIND);
  exts->action = NULL;
 }
#elif defined CONFIG_NET_CLS_POLICE
 if (exts->police) {
// 释放tcf策略
  tcf_police_release(exts->police, TCA_ACT_UNBIND);
  exts->police = NULL;
 }
#endif
}
 
int
tcf_exts_validate(struct tcf_proto *tp, struct rtattr **tb,
           struct rtattr *rate_tlv, struct tcf_exts *exts,
           struct tcf_ext_map *map)
{
// 结构清零
 memset(exts, 0, sizeof(*exts));
 
#ifdef CONFIG_NET_CLS_ACT
 {
  int err;
  struct tc_action *