/proc/net/route 파싱

본것중에 가장 간단하게 /proc/net/route를 파싱하는 소스인 듯하다.

# cat /proc/net/route Iface   Destination     Gateway         Flags   RefCnt  Use     Metric  Mask            MTU     Window  IRTT eth0    000AA8C0        00000000        0001    0       0       0       00FFFFFF        0       0       0 eth0    00000000        010AA8C0        0003    0       0       0       00000000        0       0       0 # route Kernel IP routing table Destination     Gateway         Genmask         Flags Metric Ref    Use Iface 192.168.10.0    *               255.255.255.0   U     0      0        0 eth0 default         192.168.10.1    0.0.0.0         UG    0      0        0 eth0

아무튼 route로 출력하는 default가 UG 플래그로 default gateway이며,
파일에서는 Destination과 Mask가 0x00000000 인 녀석이 default gateway이다.

#include "stdio.h"
#include "stdlib.h"
#include "unistd.h"

#define IP_PRINT(a) \
    *((unsigned char *)(&a)), \
    *(((unsigned char *)(&a)) + 1), \
    *(((unsigned char *)(&a)) + 2), \
    *(((unsigned char *)(&a)) + 3)

int main()
{
    FILE* fp = fopen("/proc/net/route", "r");
    char buf[256];
    static char iface[256];
    unsigned int destination, gateway, flags, refcnt, use, metric, mask;
    int ret;

    if (fp == NULL)
        exit(-1);

    while (fgets(buf, 255, fp)) {
        if (!strncmp(buf, "Iface", 5))
            continue;

        ret = sscanf(buf, "%s\t%x\t%x\t%d\t%d\t%d\t%d\t%x",
                    iface, &destination, &gateway, &flags,
                    &refcnt, &use, &metric, &mask);

        if (ret < 8) {
            fprintf(stderr, "ERROR: line read error\n");
            continue;
        }

        if (destination != 0) {
            fprintf(stderr, "%s: gateway %u.%u.%u.%u, "
                    "destination %u.%u.%u.%u netmask %u.%u.%u.%u\n",
                    iface,
                    IP_PRINT(gateway),
                    IP_PRINT(destination),
                    IP_PRINT(mask));
            continue;
        }

        if (mask != 0) {
            fprintf(stderr, "%s: gateway %u.%u.%u.%u, default, "
                    "but have netmask %u.%u.%u.%u???\n",
                    iface,
                    IP_PRINT(gateway),
                    IP_PRINT(mask));
            continue;
        }

        fprintf(stderr, "%s: gateway %u.%u.%u.%u, default\n",
                iface,
                IP_PRINT(gateway));
    }
    fclose(fp);
}

[링크 : http://elenoa.tistory.com/72]