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Internet协议族

2024-07-18 15:45:51 226人阅读

Linux在2.6.32版本可支持37种协议族，每个协议族用一个net_proto_family结构实例来表示，在系统初始化时，以各协议族对应的协议族为下标，调用sock_register()将结构注册到全局数组net_families[NPROTO]。此外还有一个地址族的概念，地址族用地址族常量来标识，到目前为止，协议族常量和地址族常量是一一对应的，且值相同

/include/linux/sock.h

/* Supported address families. */
#define AF_UNSPEC	0
#define AF_UNIX		1	/* Unix domain sockets 		*/
#define AF_LOCAL	1	/* POSIX name for AF_UNIX	*/
#define AF_INET		2	/* Internet IP Protocol 	*/
#define AF_AX25		3	/* Amateur Radio AX.25 		*/
#define AF_IPX		4	/* Novell IPX 			*/
#define AF_APPLETALK	5	/* AppleTalk DDP 		*/
#define AF_NETROM	6	/* Amateur Radio NET/ROM 	*/
#define AF_BRIDGE	7	/* Multiprotocol bridge 	*/
#define AF_ATMPVC	8	/* ATM PVCs			*/
#define AF_X25		9	/* Reserved for X.25 project 	*/
#define AF_INET6	10	/* IP version 6			*/
#define AF_ROSE		11	/* Amateur Radio X.25 PLP	*/
#define AF_DECnet	12	/* Reserved for DECnet project	*/
#define AF_NETBEUI	13	/* Reserved for 802.2LLC project*/
#define AF_SECURITY	14	/* Security callback pseudo AF */
#define AF_KEY		15      /* PF_KEY key management API */
#define AF_NETLINK	16
#define AF_ROUTE	AF_NETLINK /* Alias to emulate 4.4BSD */
#define AF_PACKET	17	/* Packet family		*/
#define AF_ASH		18	/* Ash				*/
#define AF_ECONET	19	/* Acorn Econet			*/
#define AF_ATMSVC	20	/* ATM SVCs			*/
#define AF_RDS		21	/* RDS sockets 			*/
#define AF_SNA		22	/* Linux SNA Project (nutters!) */
#define AF_IRDA		23	/* IRDA sockets			*/
#define AF_PPPOX	24	/* PPPoX sockets		*/
#define AF_WANPIPE	25	/* Wanpipe API Sockets */
#define AF_LLC		26	/* Linux LLC			*/
#define AF_CAN		29	/* Controller Area Network      */
#define AF_TIPC		30	/* TIPC sockets			*/
#define AF_BLUETOOTH	31	/* Bluetooth sockets 		*/
#define AF_IUCV		32	/* IUCV sockets			*/
#define AF_RXRPC	33	/* RxRPC sockets 		*/
#define AF_ISDN		34	/* mISDN sockets 		*/
#define AF_PHONET	35	/* Phonet sockets		*/
#define AF_IEEE802154	36	/* IEEE802154 sockets		*/
#define AF_MAX		37	/* For now.. */

/* Protocol families, same as address families. */
#define PF_UNSPEC	AF_UNSPEC
#define PF_UNIX		AF_UNIX
#define PF_LOCAL	AF_LOCAL
#define PF_INET		AF_INET
#define PF_AX25		AF_AX25
#define PF_IPX		AF_IPX
#define PF_APPLETALK	AF_APPLETALK
#define	PF_NETROM	AF_NETROM
#define PF_BRIDGE	AF_BRIDGE
#define PF_ATMPVC	AF_ATMPVC
#define PF_X25		AF_X25
#define PF_INET6	AF_INET6
#define PF_ROSE		AF_ROSE
#define PF_DECnet	AF_DECnet
#define PF_NETBEUI	AF_NETBEUI
#define PF_SECURITY	AF_SECURITY
#define PF_KEY		AF_KEY
#define PF_NETLINK	AF_NETLINK
#define PF_ROUTE	AF_ROUTE
#define PF_PACKET	AF_PACKET
#define PF_ASH		AF_ASH
#define PF_ECONET	AF_ECONET
#define PF_ATMSVC	AF_ATMSVC
#define PF_RDS		AF_RDS
#define PF_SNA		AF_SNA
#define PF_IRDA		AF_IRDA
#define PF_PPPOX	AF_PPPOX
#define PF_WANPIPE	AF_WANPIPE
#define PF_LLC		AF_LLC
#define PF_CAN		AF_CAN
#define PF_TIPC		AF_TIPC
#define PF_BLUETOOTH	AF_BLUETOOTH
#define PF_IUCV		AF_IUCV
#define PF_RXRPC	AF_RXRPC
#define PF_ISDN		AF_ISDN
#define PF_PHONET	AF_PHONET
#define PF_IEEE802154	AF_IEEE802154
#define PF_MAX		AF_MAX

对应不同的协议族，其传输层的结构和实现有着巨大的差异，因此其各自的套接口创建函数也会有很大区别，而通过net_proto_family结构屏蔽了这些区别，使得各个协议在初始化的时候，可以统一用sock_register()注册到net_families数组中。因此实际上net_proto_family结构提供了一个协议族到套接口创建之间的接口

net_proto_family

struct net_proto_family {
	int		family;
	int		(*create)(struct net *net, struct socket *sock, int protocol);
	struct module	*owner;
};

/**
 *	sock_register - add a socket protocol handler
 *	@ops: description of protocol
 *
 *	This function is called by a protocol handler that wants to
 *	advertise its address family, and have it linked into the
 *	socket interface. The value ops->family coresponds to the
 *	socket system call protocol family.
 */
int sock_register(const struct net_proto_family *ops)
{
	int err;

	if (ops->family >= NPROTO) {
		printk(KERN_CRIT "protocol %d >= NPROTO(%d)\n", ops->family,
		       NPROTO);
		return -ENOBUFS;
	}

	spin_lock(&net_family_lock);
	if (net_families[ops->family])
		err = -EEXIST;
	else {
		net_families[ops->family] = ops;
		err = 0;
	}
	spin_unlock(&net_family_lock);

	printk(KERN_INFO "NET: Registered protocol family %d\n", ops->family);
	return err;
}

inet_protosw

inet_protosw结构在每次创建套接口时会用到，此结构也只在套接口层起作用

/* This is used to register socket interfaces for IP protocols.  */
struct inet_protosw {
	struct list_head list;

        /* These two fields form the lookup key.  */
	unsigned short	 type;	   /* This is the 2nd argument to socket(2). */
	unsigned short	 protocol; /* This is the L4 protocol number.  */

	struct proto	 *prot;
	const struct proto_ops *ops;
  
	int              capability; /* Which (if any) capability do
				      * we need to use this socket
				      * interface?
                                      */
	char             no_check;   /* checksum on rcv/xmit/none? */
	unsigned char	 flags;      /* See INET_PROTOSW_* below.  */
};

type

标识套接口的类型，对于Internet协议族共有三种类型SOCK_STREAM、SOCK_DGRAM和SOCK_RAW，与应用程序层创建套接口函数socket()的第二个参数type取值恰好对应

protocol

标识协议族中四层协议号，Internet协议族中的值包括IPPROTO_TCP、IPPROTO_UDP等

prot

套接口网络层接口。TCP为tcp_prot;UDP为udp_prot;原始套接口raw_prot。

ops

套接口传输层接口。TCP为inet_stream_ops;UDP为inet_dgram_ops;原始套接口inet_sockraw_ops。

capability

当大于零时，需要检验当前创建套接口的进程是否有这种能力。

flags

INET_PROTOSW_REUSE 标识端口是否能被重用

INET_PROTOSW_PERMANENT 标识此协议不能被替换或卸载

INET_PROTOSW_ICSK 标识是不是连续的套接口

inet_register_protosw()将inet_protosw实例注册到inet_sw散列表中，而inet_unregister_protosw()可以将指定的inet_protosw实例从inetsw散列表中注销，但是注意：被标识为INET_PROTOSW_PERMANENT的inet_protosw实例不能重载或注销。

void inet_register_protosw(struct inet_protosw *p)
{
	struct list_head *lh;
	struct inet_protosw *answer;
	int protocol = p->protocol;
	struct list_head *last_perm;

	spin_lock_bh(&inetsw_lock);

	if (p->type >= SOCK_MAX)
		goto out_illegal;

	/* If we are trying to override a permanent protocol, bail. */
	answer = NULL;
	last_perm = &inetsw[p->type];
	list_for_each(lh, &inetsw[p->type]) {
		answer = list_entry(lh, struct inet_protosw, list);

		/* Check only the non-wild match. */
		if (INET_PROTOSW_PERMANENT & answer->flags) {
			if (protocol == answer->protocol)
				break;
			last_perm = lh;
		}

		answer = NULL;
	}
	if (answer)
		goto out_permanent;

	/* Add the new entry after the last permanent entry if any, so that
	 * the new entry does not override a permanent entry when matched with
	 * a wild-card protocol. But it is allowed to override any existing
	 * non-permanent entry.  This means that when we remove this entry, the
	 * system automatically returns to the old behavior.
	 */
	list_add_rcu(&p->list, last_perm);
out:
	spin_unlock_bh(&inetsw_lock);

	return;

out_permanent:
	printk(KERN_ERR "Attempt to override permanent protocol %d.\n",
	       protocol);
	goto out;

out_illegal:
	printk(KERN_ERR
	       "Ignoring attempt to register invalid socket type %d.\n",
	       p->type);
	goto out;
}

net_protocol

net_protocol是一个非常重要的结构，定义了协议族中支持的传输层协议以及传输层的报文接收例程。此结构是网络层和传输层之前的桥梁，当网络数据报文从网络层流向传输层时，会调用此结构中的传输层协议数据报接收处理函数。

/* This is used to register protocols. */
struct net_protocol {
	int			(*handler)(struct sk_buff *skb);
	void			(*err_handler)(struct sk_buff *skb, u32 info);
	int			(*gso_send_check)(struct sk_buff *skb);
	struct sk_buff	       *(*gso_segment)(struct sk_buff *skb,
					       int features);
	struct sk_buff	      **(*gro_receive)(struct sk_buff **head,
					       struct sk_buff *skb);
	int			(*gro_complete)(struct sk_buff *skb);
	unsigned int		no_policy:1,
				netns_ok:1;
};

int (*handler)(struct sk_buff *skb)

传输层协议数据报接收处理函数，当网络层接收IP数据报之后，根据IP数据报所指示传输层协议，调用对应传输层net_protocol结构的该例程接收报文。

void (*err_handler)(struct sk_buff *skb, u32 info)
在ICMP模块中接收到差错报文后，会解析差错报文，并根据差错报文中原始的IP首部，调用对应传输层的异常处理函数err_handler()。

int (*gso_send_check)(struct sk_buff *skb);

struct sk_buff *(*gso_segment)(struct sk_buff *skb, int features);

GSO是网络设备支持传输层的一个功能

当GSO数据报输出时到达网络设备，如果网络设备不支持GSO的情况，则需要传输层对输出的数据报重新进行GSO分段和校验和的计算。因此需要网络层提供接口给设备层，能够访问到传输层的GSO分段和校验和的计算功能，对输出的数据报进行分段和执行校验和

unsigned int no_policy

标识在路由时是否进行策略路由，TCP和UDP默认不进行策略路由

内核中为Internet协议定义了4个net_protocol结构实例-------icmp_protocol,udp_protocol,tcp_protocol,igmp_protocol,分别于ICMP、UDP、TCP、IGMP协议一一对应。在Internet协议族初始化时，调用inet_add_protocol()将它们注册到net_protocol结构指针数组inet_protos[MAX_INET_PROTOS]中，在系统运行过程中，随时可以用内核模块加载/卸载的方式，调用函数inet_add_protocol/inet_del_protocol将net_protocol结构实例注册到inet_protos[]数组中，或从中删除。

Internet协议族的初始化

Internet协议族的初始化函数为inet_init(),通过fs_initcall(inet_init),将inet_init()加到内核的初始化列表中，保证了此函数会在系统启动时被调用

static int __init inet_init(void)
{
	struct sk_buff *dummy_skb;
	struct inet_protosw *q;
	struct list_head *r;
	int rc = -EINVAL;

	BUILD_BUG_ON(sizeof(struct inet_skb_parm) > sizeof(dummy_skb->cb));

	rc = proto_register(&tcp_prot, 1);
	if (rc)
		goto out;

	rc = proto_register(&udp_prot, 1);
	if (rc)
		goto out_unregister_tcp_proto;

	rc = proto_register(&raw_prot, 1);
	if (rc)
		goto out_unregister_udp_proto;

	/*
	 *	Tell SOCKET that we are alive...
	 */

	(void)sock_register(&inet_family_ops);

#ifdef CONFIG_SYSCTL
	ip_static_sysctl_init();
#endif

	/*
	 *	Add all the base protocols.
	 */

	if (inet_add_protocol(&icmp_protocol, IPPROTO_ICMP) < 0)
		printk(KERN_CRIT "inet_init: Cannot add ICMP protocol\n");
	if (inet_add_protocol(&udp_protocol, IPPROTO_UDP) < 0)
		printk(KERN_CRIT "inet_init: Cannot add UDP protocol\n");
	if (inet_add_protocol(&tcp_protocol, IPPROTO_TCP) < 0)
		printk(KERN_CRIT "inet_init: Cannot add TCP protocol\n");
#ifdef CONFIG_IP_MULTICAST
	if (inet_add_protocol(&igmp_protocol, IPPROTO_IGMP) < 0)
		printk(KERN_CRIT "inet_init: Cannot add IGMP protocol\n");
#endif

	/* Register the socket-side information for inet_create. */
	for (r = &inetsw[0]; r < &inetsw[SOCK_MAX]; ++r)
		INIT_LIST_HEAD(r);

	for (q = inetsw_array; q < &inetsw_array[INETSW_ARRAY_LEN]; ++q)
		inet_register_protosw(q);

	/*
	 *	Set the ARP module up
	 */

	arp_init();

	/*
	 *	Set the IP module up
	 */

	ip_init();

	tcp_v4_init();

	/* Setup TCP slab cache for open requests. */
	tcp_init();

	/* Setup UDP memory threshold */
	udp_init();

	/* Add UDP-Lite (RFC 3828) */
	udplite4_register();

	/*
	 *	Set the ICMP layer up
	 */

	if (icmp_init() < 0)
		panic("Failed to create the ICMP control socket.\n");

	/*
	 *	Initialise the multicast router
	 */
#if defined(CONFIG_IP_MROUTE)
	if (ip_mr_init())
		printk(KERN_CRIT "inet_init: Cannot init ipv4 mroute\n");
#endif
	/*
	 *	Initialise per-cpu ipv4 mibs
	 */

	if (init_ipv4_mibs())
		printk(KERN_CRIT "inet_init: Cannot init ipv4 mibs\n");

	ipv4_proc_init();

	ipfrag_init();

	dev_add_pack(&ip_packet_type);

	rc = 0;
out:
	return rc;
out_unregister_udp_proto:
	proto_unregister(&udp_prot);
out_unregister_tcp_proto:
	proto_unregister(&tcp_prot);
	goto out;
}

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