linux下通过netlink 获取系统路由及接口地址信息

platform: ubuntu 8.10 server

gcc version: gcc version 4.3.2

#include <linux/types.h>
#include <asm/types.h>
#include <inttypes.h>
#include <sys/file.h>
#include <sys/user.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <linux/if.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <stdbool.h>
#include <errno.h>

typedef uint32_t u32;
typedef uint16_t u16;

struct nlsock {
    int sock;
    int seq;
    struct sockaddr_nl snl;
    char *name;
} nl_cmd = { -1, 0, {0}, "netlink-cmd" };

static int index_oif = 0;
struct nl_if_info {
    u32 addr;
    char *name;
};
static int nl_socket ( struct nlsock *nl, unsigned long groups )
{
    int ret;
    struct sockaddr_nl snl;
    int sock;
    int namelen;

    sock = socket ( AF_NETLINK, SOCK_RAW, NETLINK_ROUTE );
    if ( sock < 0 ) {
        fprintf ( stderr,  "Can't open %s socket: %s", nl->name,
                strerror ( errno ) );
        return -1;
    }

    ret = fcntl ( sock, F_SETFL, O_NONBLOCK );
    if ( ret < 0 ) {
        fprintf ( stderr,  "Can't set %s socket flags: %s", nl->name,
                strerror ( errno ) );
        close ( sock );
        return -1;
    }

    memset ( &snl, 0, sizeof snl );
    snl.nl_family = AF_NETLINK;
    snl.nl_groups = groups;

    /* Bind the socket to the netlink structure for anything. */
    ret = bind ( sock, ( struct sockaddr * ) &snl, sizeof snl );
    if ( ret < 0 ) {
        fprintf ( stderr,  "Can't bind %s socket to group 0x%x: %s",
                nl->name, snl.nl_groups, strerror ( errno ) );
        close ( sock );
        return -1;
    }

    /* multiple netlink sockets will have different nl_pid */
    namelen = sizeof snl;
    ret = getsockname ( sock, ( struct sockaddr * ) &snl, &namelen );
    if ( ret < 0 || namelen != sizeof snl ) {
        fprintf ( stderr,  "Can't get %s socket name: %s", nl->name,
                strerror ( errno ) );
        close ( sock );
        return -1;
    }

    nl->snl = snl;
    nl->sock = sock;
    return ret;
}

static int nl_request ( int family, int type, struct nlsock *nl )
{
    int ret;
    struct sockaddr_nl snl;

    struct {
        struct nlmsghdr nlh;
        struct rtgenmsg g;
    } req;


    /* Check netlink socket. */
    if ( nl->sock < 0 ) {
        fprintf ( stderr, "%s socket isn't active.", nl->name );
        return -1;
    }

    memset ( &snl, 0, sizeof snl );
    snl.nl_family = AF_NETLINK;

    req.nlh.nlmsg_len = sizeof req;
    req.nlh.nlmsg_type = type;
    req.nlh.nlmsg_flags = NLM_F_ROOT | NLM_F_MATCH | NLM_F_REQUEST;
    req.nlh.nlmsg_pid = 0;
    req.nlh.nlmsg_seq = ++nl->seq;
    req.g.rtgen_family = family;

    ret = sendto ( nl->sock, ( void* ) &req, sizeof req, 0,
            ( struct sockaddr* ) &snl, sizeof snl );
    if ( ret < 0 ) {
        fprintf ( stderr, "%s sendto failed: %s", nl->name, strerror ( errno ) );
        return -1;
    }
    return 0;
}

/* Receive message from netlink interface and pass those information
   to the given function. */
static int
nl_parse_info ( int ( *filter ) ( struct sockaddr_nl *, struct nlmsghdr *, void * ),
        struct nlsock *nl, void *arg )
{
    int status;
    int ret = 0;
    int error;

    while ( 1 ) {
        char buf[4096];
        struct iovec iov = { buf, sizeof buf };
        struct sockaddr_nl snl;
        struct msghdr msg = { ( void* ) &snl, sizeof snl, &iov, 1, NULL, 0, 0};
        struct nlmsghdr *h;

        status = recvmsg ( nl->sock, &msg, 0 );

        if ( status < 0 ) {
            if ( errno == EINTR )
                continue;
            if ( errno == EWOULDBLOCK || errno == EAGAIN )
                break;
            fprintf ( stderr, "%s recvmsg overrun", nl->name );
            continue;
        }

        if ( snl.nl_pid != 0 ) {
            fprintf ( stderr, "Ignoring non kernel message from pid %u",
                    snl.nl_pid );
            continue;
        }

        if ( status == 0 ) {
            fprintf ( stderr, "%s EOF", nl->name );
            return -1;
        }

        if ( msg.msg_namelen != sizeof snl ) {
            fprintf ( stderr, "%s sender address length error: length %d",
                    nl->name, msg.msg_namelen );
            return -1;
        }

        for ( h = ( struct nlmsghdr * ) buf; NLMSG_OK ( h, status );
                h = NLMSG_NEXT ( h, status ) ) {
            /* Finish of reading. */
            if ( h->nlmsg_type == NLMSG_DONE )
                return ret;

            /* Error handling. */
            if ( h->nlmsg_type == NLMSG_ERROR ) {
                struct nlmsgerr *err = ( struct nlmsgerr * ) NLMSG_DATA ( h );

                /* If the error field is zero, then this is an ACK */
                if ( err->error == 0 ) {
                    /* return if not a multipart message, otherwise continue */
                    if ( ! ( h->nlmsg_flags & NLM_F_MULTI ) ) {
                        return 0;
                    }
                    continue;
                }

                if ( h->nlmsg_len < NLMSG_LENGTH ( sizeof ( struct nlmsgerr ) ) ) {
                    fprintf ( stderr, "%s error: message truncated",
                            nl->name );
                    return -1;
                }
                fprintf ( stderr, "%s error: %s, type=%u, seq=%u, pid=%d",
                        nl->name, strerror ( -err->error ),
                        err->msg.nlmsg_type, err->msg.nlmsg_seq,
                        err->msg.nlmsg_pid );
                /*
                ret = -1;
                continue;
                */
                return -1;
            }


            /* skip unsolicited messages originating from command socket */
            if ( nl != &nl_cmd && h->nlmsg_pid == nl_cmd.snl.nl_pid ) {
                continue;
            }

            error = ( *filter ) ( &snl, h, arg );
            if ( error < 0 ) {
                fprintf ( stderr, "%s filter function error\n", nl->name );
                ret = error;
            }
        }

        /* After error care. */
        if ( msg.msg_flags & MSG_TRUNC ) {
            fprintf ( stderr, "%s error: message truncated", nl->name );
            continue;
        }
        if ( status ) {
            fprintf ( stderr, "%s error: data remnant size %d", nl->name,
                    status );
            return -1;
        }
    }
    return ret;
}

static void nl_parse_rtattr ( struct rtattr **tb, int max, struct rtattr *rta, int len )
{
    while ( RTA_OK ( rta, len ) ) {
        if ( rta->rta_type <= max )
            tb[rta->rta_type] = rta;
        rta = RTA_NEXT ( rta,len );
    }
}

static int nl_get_oif ( struct sockaddr_nl *snl, struct nlmsghdr *h, void *arg )
{
    int len;
    struct rtmsg *rtm;
    struct rtattr *tb [RTA_MAX + 1];
    u_char flags = 0;

    char anyaddr[16] = {0};

    int index;
    int table;
    void *dest;
    void *gate;

    rtm = NLMSG_DATA ( h );

    if ( h->nlmsg_type != RTM_NEWROUTE )
        return 0;
    if ( rtm->rtm_type != RTN_UNICAST )
        return 0;

    table = rtm->rtm_table;

    len = h->nlmsg_len - NLMSG_LENGTH ( sizeof ( struct rtmsg ) );
    if ( len < 0 )
        return -1;

    memset ( tb, 0, sizeof tb );
    nl_parse_rtattr ( tb, RTA_MAX, RTM_RTA ( rtm ), len );

    if ( rtm->rtm_flags & RTM_F_CLONED )
        return 0;
    if ( rtm->rtm_protocol == RTPROT_REDIRECT )
        return 0;
    if ( rtm->rtm_protocol == RTPROT_KERNEL )
        return 0;

    if ( rtm->rtm_src_len != 0 )
        return 0;

 

    // 这里可以对所有路由进行识别

 

    // 取得out interface index

    if ( tb[RTA_OIF] ) {
        index = * ( int * ) RTA_DATA ( tb[RTA_OIF] );
    }

    if ( tb[RTA_DST] )
        dest = RTA_DATA ( tb[RTA_DST] );
    else
        dest = anyaddr;

    /* Multipath treatment is needed. */
    if ( tb[RTA_GATEWAY] )
        gate = RTA_DATA ( tb[RTA_GATEWAY] );

 

    // 判断是否为默认路由

    if ( dest == anyaddr && gate ) {
        if ( arg != NULL ) {
            * ( int * ) arg = index;
            return 0;
        }
    }
    return 0;
}

static int nl_get_if_addr ( struct sockaddr_nl *snl, struct nlmsghdr *h, void *arg )
{
    int len;
    struct ifaddrmsg *ifa;
    struct rtattr *tb [IFA_MAX + 1];
    void *addr = NULL;
    void *broad = NULL;
    u_char flags = 0;
    char *label = NULL;
 u32 ifa_addr, ifa_local;
 char ifa_label[IFNAMSIZ + 1];
 
    ifa = NLMSG_DATA ( h );
    if ( ifa->ifa_family != AF_INET )
     return 0;
     
    if ( h->nlmsg_type != RTM_NEWADDR && h->nlmsg_type != RTM_DELADDR )
        return 0;

    len = h->nlmsg_len - NLMSG_LENGTH ( sizeof ( struct ifaddrmsg ) );
    if ( len < 0 )
        return -1;

    memset ( tb, 0, sizeof tb );

    nl_parse_rtattr ( tb, IFA_MAX, IFA_RTA ( ifa ), len );
    
    if (tb[IFA_ADDRESS] == NULL)
  tb[IFA_ADDRESS] = tb[IFA_LOCAL];
  
    if ( tb[IFA_ADDRESS] )
     ifa_addr = *(u32 *) RTA_DATA ( tb[IFA_ADDRESS] );
     
    if ( tb[IFA_LOCAL] )
     ifa_local = *(u32 *) RTA_DATA ( tb[IFA_LOCAL] );
    
    if ( tb[IFA_LABEL] )
     strncpy( ifa_label, RTA_DATA ( tb[IFA_LABEL] ), IFNAMSIZ ); 
     

    // 打印所有地址信息
    printf( "addr=%08x loal=%08x name=%s\n", 
     ifa_addr,
     ifa_local,
     ifa_label );
    return 0;
}

int main()
{
    int ret;
    char if_name[PAGE_SIZE];
    char *p;
    struct nl_if_info if_info = { -1, "eth0" };

    ret = nl_socket ( &nl_cmd, 0 );
    if ( ret < 0 ) {
        return ret;
    }
    ret = nl_request ( AF_INET, RTM_GETROUTE, &nl_cmd );
    if ( ret < 0 ) {
        return ret;
    }
    ret = nl_parse_info ( nl_get_oif, &nl_cmd, &index_oif );
    if ( ret < 0 )
        return ret;

    printf ( "oif=%08x \n", index_oif );
    if ( index_oif > 0 ) {
     p = if_indextoname ( index_oif, if_name );
     if ( p ) {
         printf ( "interface=%s\n", p );
     }
 }

    ret = nl_request ( AF_INET, RTM_GETADDR, &nl_cmd );
    if ( ret < 0 )
        return ret;
 
    ret = nl_parse_info ( nl_get_if_addr, &nl_cmd, &if_info );
    if ( ret < 0 )
        return ret;
    

    return 0;
}

参考:

1> RFC3549 - Linux Netlink as an IP Services Protocol

2> Zebra Source code

3> netlink(7) - Linux man page