結構原型:

/*
?* Interface request structure used for socket
?* ioctl's.? All interface ioctl's must have parameter
?* definitions which begin with ifr_name.? The
?* remainder may be interface specific.
?*/

struct?ifreq?
{
#define?IFHWADDRLEN?6
?union
?{
??char?ifrn_name[IFNAMSIZ];??/* if name, e.g. "en0" */
?} ifr_ifrn;
?
?union?{
??struct?sockaddr ifru_addr;
??struct?sockaddr ifru_dstaddr;
??struct?sockaddr ifru_broadaddr;
??struct?sockaddr ifru_netmask;
??struct? sockaddr ifru_hwaddr;
??short?ifru_flags;
??int?ifru_ivalue;
??int?ifru_mtu;
??struct? ifmap ifru_map;
??char?ifru_slave[IFNAMSIZ];?/* Just fits the size */
??char?ifru_newname[IFNAMSIZ];
??void?__user *?ifru_data;
??struct?if_settings ifru_settings;
?} ifr_ifru;
};

#define?ifr_name?ifr_ifrn.ifrn_name?/* interface name ?*/
#define?ifr_hwaddr?ifr_ifru.ifru_hwaddr?/* MAC address ??*/
#define?ifr_addr?ifr_ifru.ifru_addr?/* address??*/
#define?ifr_dstaddr?ifr_ifru.ifru_dstaddr?/* other end of p-p lnk?*/
#define?ifr_broadaddr?ifr_ifru.ifru_broadaddr?/* broadcast address?*/
#define?ifr_netmask?ifr_ifru.ifru_netmask?/* interface net mask?*/
#define?ifr_flags?ifr_ifru.ifru_flags?/* flags??*/
#define?ifr_metric?ifr_ifru.ifru_ivalue?/* metric??*/
#define?ifr_mtu??ifr_ifru.ifru_mtu?/* mtu???*/
#define?ifr_map??ifr_ifru.ifru_map?/* device map??*/
#define?ifr_slave?ifr_ifru.ifru_slave?/* slave device??*/
#define?ifr_data?ifr_ifru.ifru_data?/* for use by interface?*/
#define?ifr_ifindex?ifr_ifru.ifru_ivalue?/* interface index?*/
#define?ifr_bandwidth?ifr_ifru.ifru_ivalue????/* link bandwidth?*/
#define?ifr_qlen?ifr_ifru.ifru_ivalue?/* Queue length ?*/
#define?ifr_newname?ifr_ifru.ifru_newname?/* New name??*/
#define?ifr_settings?ifr_ifru.ifru_settings?/* Device/proto settings*/

基本介紹:?

ifreq結構定義在/usr/include/net/if.h，用來配置ip地址，激活接口，配置MTU等接口信息的。其中包含了一個接口的名字和具體內容——（是個共用體，有可能是IP地址，廣播地址，子網(wǎng)掩碼，MAC號，MTU或其他內容）。ifreq包含在ifconf結構中。而ifconf結構通常是用來保存所有接口的信息的。

舉例說明：

在Linux系統(tǒng)中，ifconfig命令是通過ioctl接口與內核通信，例如，當系統(tǒng)管理員輸入如下命令來改變接口eth0的MTU大?。?/p>

ifconfig eth0 mtu 1250

ifconfig命令首先打開一個socket，然后通過系統(tǒng)管理員輸入的參數(shù)初始化一個數(shù)據(jù)結構，并通過ioctl調用將數(shù)據(jù)傳送到內核。SIOCSIFMTU是命令標識符。

struct?ifreq?data;
??? fd = socket(PF_INET,?SOCK_DGRAM, 0);
????< ... initialize "data" ...>
??? err = ioctl(fd, SIOCSIFMTU, &data);

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