netlink与rtnetlink（二）

转至：http://blogold.chinaunix.net/u/15993/showart_90109.html

rtnetlink就是一组操作rtnetlink消息的宏。
在netlink中，初始化一个netlink_route套接字时，最后一个字段使用NETLINK_ROUTE时就是rtnetlink_socket。
 #include <asm/types.h>
        #include <linux/netlink.h>
        #include <linux/rtnetlink.h>
        #include <sys/socket.h>
        rtnetlink_socket  =  socket(PF_NETLINK, int  socket_type, NETLINK_ROUTE);
这组宏包括：
 int RTA_OK(struct rtattr *rta, int rtabuflen);
        void *RTA_DATA(struct rtattr *rta);
        unsigned int RTA_PAYLOAD(struct rtattr *rta);
        struct rtattr *RTA_NEXT(struct rtattr *rta,  unsigned  int  rtabuflen);
        unsigned int RTA_LENGTH(unsigned int length);
        unsigned int RTA_SPACE(unsigned int length);

使用这一组宏可以对路由表进行读写和修改。不仅对路由表，还有很多网络参数都可以通过rtnetlink来修改。

路由属性：
一些rtnetlink消息在初始化头后面有附加的属性：
 struct rtattr
       {
    unsigned short rta_len;     /* Length of option */
    unsigned short rta_type;    /* Type of option */
    /* Data follows */
       };

除了标准的netlink消息之外，rtnetlink由这些消息类型组成。
RTM_NEWLINK, RTM_DELLINK, RTM_GETLINK
 创建或者删除一个特定的网络接口，或者从一个特定的网络接口上获得信息。这些消息含有一个ifinfomsg类型的结构，紧跟在后面的是一系列的rtattr结构。
 struct ifinfomsg
 {
  unsigned char  ifi_family;  /* AF_UNSPEC */
  unsigned char  __ifi_pad;   /* unused */
  unsigned short ifi_type;    /* Device type */
  int   ifi_index;   /* Interface index   */
  unsigned int  ifi_flags;   /* Device flags  */
  unsigned int  ifi_change;  /* change mask */
 } 
 其中ifi_change是为将来预留的，总是被设为0xFFFFFFFF
       rta_type     value type       description
       --------------------------------------------------------------
       IFLA_UNSPEC    -        unspecified.
       IFLA_ADDRESS    hardware address   interface L2 address
       IFLA_BROADCAST    hardware address   L2 broadcast address.
       IFLA_IFNAME    asciiz string      Device name.
       IFLA_MTU     unsigned int       MTU of the device.
       IFLA_LINK     int        Link type.
       IFLA_QDISC    asciiz string      Queueing discipline.
       IFLA_STATS    struct       Interface Statistics.
       net_device_stats
RTM_NEWADDR, RTM_DELADDR, RTM_GETADDR
 添加,删除或者接收一个和接口相关的IP地址的信息。在linux2.2中，一个网口是可以有多个IP地址信息的。这些消息含有一个ifaddrmsg类型的结构，紧跟在后面的是一系列的rtattr结构。
 struct ifaddrmsg
       {
    unsigned char  ifa_family;  /* Address type */
    unsigned char  ifa_prefixlen;/* Prefixlength of the address */
    unsigned char  ifa_flags;   /* Address flags */
    unsigned char  ifa_scope;   /* Address scope */
    int   ifa_index;   /* Interface index   */
       };
   rta_type       value type      description
       -------------------------------------------------------------
       IFA_UNSPEC      -        unspecified.
       IFA_ADDRESS     raw protocol address   interface address
       IFA_LOCAL       raw protocol address   local address
       IFA_LABEL       asciiz string      name of the interface
       IFA_BROADCAST   raw protocol address   broadcast address.
       IFA_ANYCAST     raw protocol address   anycast address
       IFA_CACHEINFO   struct ifa_cacheinfo   Address information.

RTM_NEWROUTE, RTM_DELROUTE, RTM_GETROUTE
 创建,删除一个网络路由或者从一个网络路由上获得信息。这些消息包含了一个rtmsg结构，紧跟着的是一系列的rtattr结构，这是可选的。
  struct rtmsg
       {
    unsigned char  rtm_family;  /* Address family of route */
    unsigned char  rtm_dst_len; /* Length of source */
    unsigned char  rtm_src_len; /* Length of destination */
    unsigned char  rtm_tos;     /* TOS filter */

    unsigned char  rtm_table;   /* Routing table id */
    unsigned char  rtm_protocol;/* Routing protocol; see below */
    unsigned char  rtm_scope;   /* See below */
    unsigned char  rtm_type;    /* See below */

    unsigned int  rtm_flags;
       };

       rtm_type  Route type
       -----------------------------------------------------------
       RTN_UNSPEC unknown route
       RTN_UNICAST a gateway or direct route
       RTN_LOCAL  a local interface route
       RTN_BROADCAST a  local  broadcast  route  (sent  as  a
    broadcast)
       RTN_ANYCAST a local broadcast route (sent as a  uni-
    cast)
       RTN_MULTICAST a multicast route
       RTN_BLACKHOLE a packet dropping route
       RTN_UNREACHABLE an unreachable destination
       RTN_PROHIBIT a packet rejection route
       RTN_THROW  continue routing lookup in another table
       RTN_NAT  a network address translation rule
       RTN_XRESOLVE refer to  an external  resolver  (not
    implemented)

       rtm_protocol Route origin.
       -----------------------------------------
       RTPROT_UNSPEC unknown
       RTPROT_REDIRECT by  an ICMP  redirect
    (currently unused)
       RTPROT_KERNEL by the kernel
       RTPROT_BOOT during boot
       RTPROT_STATIC by the administrator
 比RTPROT_STATIC大的值就不会再被kernel解释了，他们就只是用于用户信息了。

       rtm_scope为到目标的距离
       RT_SCOPE_UNIVERSE   global route
       RT_SCOPE_SITE   interior   route  in the
      local autonomous system
       RT_SCOPE_LINK   route on this link
       RT_SCOPE_HOST   route on the local host
       RT_SCOPE_NOWHERE   destination doesn't exist

       RT_SCOPE_UNIVERSE到RT_SCOPE_SITE之间的值是对用户可得的。

       The rtm_flags有以下一些含义：
       RTM_F_NOTIFY     if  the route changes, notify the user via
          rtnetlink
       RTM_F_CLONED     route is cloned from another route
       RTM_F_EQUALIZE   a multicast equalizer (not yet implemented)

       rtm_table表明了路由表
       RT_TABLE_UNSPEC  an unspecified routing table
       RT_TABLE_DEFAULT  the default table
       RT_TABLE_MAIN  the main table
       RT_TABLE_LOCAL  the local table

       用户可以分配RT_TABLE_UNSPEC和RT_TABLE_DEFAULT之间任意的值。

       属性
       rta_type       value type  description
       --------------------------------------------------------------
       RTA_UNSPEC      -    ignored.
       RTA_DST       protocol address  Route destination address.
       RTA_SRC       protocol address  Route source address.
       RTA_IIF       int   Input interface index.
       RTA_OIF       int   Output interface index.
       RTA_GATEWAY     protocol address  The gateway of the route
       RTA_PRIORITY    int   Priority of route.
       RTA_PREFSRC
       RTA_METRICS     int   Route metric
       RTA_MULTIPATH
       RTA_PROTOINFO
       RTA_FLOW
       RTA_CACHEINFO

 RTM_NEWNEIGH, RTM_DELNEIGH, RTM_GETNEIGH
 RTM_NEWQDISC, RTM_DELQDISC, RTM_GETQDISC
 RTM_NEWTCLASS, RTM_DELTCLASS, RTM_GETTCLASS
 RTM_NEWTFILTER, RTM_DELTFILTER, RTM_GETTFILTER

 这四组宏我就不一一介绍了，大家可以man一下。