ifreq和ifconf

﹏ヽ暗。殇╰゛Y 2022-05-08 09:18 204阅读 0赞

### 一、文件 ###

*  /usr/include/net/if.h

### 二、作用 ###

*  ifreq用来配置ip地址，激活接口，配置MTU等接口信息的。其中包含了一个接口的名 字和具体内容（是个共用体，有可能是IP地址，广播地址，子网掩码，MAC号，MTU或其他内容）。
 *  ifreq包含在ifconf结构中。而 ifconf结构通常是用来保存所有接口的信息的。

/*
     * 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.
     * 用于socket ioctl的接口请求结构。使用这些接口都必须在ifr_name参数被定义的情况下
     */
    
    struct ifreq {
    #define IFHWADDRLEN	6
    	union
    	{
    		char	ifrn_name[IFNAMSIZ];		/* if name, e.g. "en0" */
    	} ifr_ifrn;
    	
    	union {
    		struct	sockaddr ifru_addr;/* address		*/
    		struct	sockaddr ifru_dstaddr; /*????*/
    		struct	sockaddr ifru_broadaddr; /*广播地址*/
    		struct	sockaddr ifru_netmask;/*子网掩码*/
    		struct  sockaddr ifru_hwaddr; /* MAC address 		*/
    		short	ifru_flags;
    		int	ifru_ivalue;
    		int	ifru_mtu; /*是指一种通信协议的某一层上面所能通过的最大数据包大小(以字节为单位)*/
    		struct  ifmap ifru_map;
    		char	ifru_slave[IFNAMSIZ];	/* Just fits the size */
    		char	ifru_newname[IFNAMSIZ];
    		void __user *	ifru_data; /*当前被使用的接口*/
    		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*/
    
    /*
     * Structure used in SIOCGIFCONF request.
     * Used to retrieve interface configuration
     * for machine (useful for programs which
     * must know all networks accessible).
     * 用于检索机器的接口配置
     */
    
    struct ifconf  {
    	int	ifc_len;			/* size of buffer	*/
    	union {
    		char __user *ifcu_buf;
    		struct ifreq __user *ifcu_req;
    	} ifc_ifcu;
    };
    #define	ifc_buf	ifc_ifcu.ifcu_buf		/* buffer address	*/
    #define	ifc_req	ifc_ifcu.ifcu_req		/* array of structures	*/

### 三、举例 ###

*  在Linux系统中，ifconfig命令是通过ioctl接口与内核通信，例如，当系统管理员输入如下命令来改变接口eth0的MTU大小：

ifconfig eth0 mtu 1250

*  ifconfig命令首先打开一个socket，然后通过系统管理员输入的参数初始化一个数据结构，并通过ioctl调用将数据传送到内核。SIOCSIFMTU是命令标识符。

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