list_for_each_entry详解

<span style="font-size:18px;">先上相关代码：</span>

<pre name="code" class="cpp">/**
 * list_for_each_entry_rcu	-	iterate over rcu list of given type
 * @pos:	the type * to use as a loop cursor.
 * @head:	the head for your list.
 * @member:	the name of the list_struct within the struct.
 *
 * This list-traversal primitive may safely run concurrently with
 * the _rcu list-mutation primitives such as list_add_rcu()
 * as long as the traversal is guarded by rcu_read_lock().
 */
#define list_for_each_entry_rcu(pos, head, member) 
	for (pos = list_entry_rcu((head)->next, typeof(*pos), member); 
		prefetch(pos->member.next), &pos->member != (head); 
		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))

上面用到了list_entry_rcu()，上代码：

/**
 * list_entry_rcu - get the struct for this entry
 * @ptr:        the &struct list_head pointer.
 * @type:       the type of the struct this is embedded in.
 * @member:     the name of the list_struct within the struct.
 *
 * This primitive may safely run concurrently with the _rcu list-mutation
 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
 */
#define list_entry_rcu(ptr, type, member) 
	container_of(rcu_dereference(ptr), type, member)

list_entry_rcu作用：根据指向结构体type中成员member的指针ptr，返回指向该结构体的指针。prefetch(pos->member.next)：通知CPU将（）内的数据预取，以提高效率。判断条件：&pos->member != (head)list_for_each_entry_rcu的作用：head为链表的头，它作为一个成员member被包含在pos指向的结构体中，从head开始遍历链表，直到pos又指向包含head的结构体，停止遍历。

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