这个例程首先检查传递的查询上下文是否非null，以及是否是用于组成员查询的上下文。
Initially, this routine checks if the passed inquiry context is not NULL and is for a group member inquiry.
多路广播路由器会发送“组成员查询”消息，以了解哪些组在每个所连接到的物理网络上都有成员。
Multicast routers send group Membership Query messages to learn which groups have members on each of their attached physical networks.
查询上下文只是一个结构的指针，在内部维护这个结构，用于查询组成员、概要、塔或uuid成员。
An inquiry context is nothing but a pointer to the structure that is maintained internally for inquiries made on group members, profiles, towers or uuid members.
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