找到一个可用的数字

转载于 2017-02-28 17:10:50 发布 · 362 阅读

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源码来自Linux 桥模块

/* find an available port number */
static int find_portno(struct net_bridge *br)
{
	int index;
	struct net_bridge_port *p;
	unsigned long *inuse;

	inuse = kcalloc(BITS_TO_LONGS(BR_MAX_PORTS), sizeof(unsigned long),
			GFP_KERNEL);
	if (!inuse)
		return -ENOMEM;

	set_bit(0, inuse);	/* zero is reserved */
	list_for_each_entry(p, &br->port_list, list) {
		set_bit(p->port_no, inuse);//当前可用的端口号进行位设置
	}
	index = find_first_zero_bit(inuse, BR_MAX_PORTS);//找到未设置的index
	kfree(inuse);

	return (index >= BR_MAX_PORTS) ? -EXFULL : index;
}