[C]關於 ioctl 跟 ifreq

ioctl() 是提供對device作input/output control的system call, 根據deivce的不同所實作的參數也不同, 但前兩個是固定的.
<code>int ioctl(int d, int request, ...)</code>
主要有3個參數:
1. d: descriptor, 是透過open()某個device而得到的handle(linux稱descriptor而windows稱handle), 主要是描述該deivice的abstract indicator.
2. request: 根據不同的device提供的request也不同
ex.
SIOCGIFADDRS - Gets the list of addresses associated with an interface.
SIOCGIFADDR  - gets an interface address
取得本機位址
 int sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
 struct ifreq ifr;
 ifr.ifr_addr.sa_family = AF_INET;
 strncpy(ifr.ifr_name, "eth0", IFNAMSIZ-1);
 ioctl(sock_fd, SIOCGIFADDRS, &ifr);

另外就是 ifreq 是指用來config network device的結構

struct ifreq {
    char    ifr_name[IFNAMSIZ];/* Interface name */
    union {
            struct sockaddrifr_addr;
            struct sockaddrifr_dstaddr;
            struct sockaddrifr_broadaddr;
            struct sockaddrifr_netmask;
            struct sockaddrifr_hwaddr;
            short   ifr_flags;
            int     ifr_ifindex;
            int     ifr_metric;
            int     ifr_mtu;
            struct ifmapifr_map;
            char    ifr_slave[IFNAMSIZ];
            char    ifr_newname[IFNAMSIZ];
            char *  ifr_data;
    };
};
struct ifconf {
    int ifc_len;    /* size of buffer */
    union {           
            char *  ifc_buf; /* buffer address */
            struct ifreq *ifc_req; /* array of structures */
    }; 
};


參考