Understand and learn to use the IFREQ structure in Linux

Prototype: / * * 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; Be 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 * / basic introduction: The IFREQ structure is defined in /usr/include/net/IF.h, configuring an IP address, activating interface, configuring an interface information such as an MTU. It contains an interface name and specific content - (is a common body, it is possible to be an IP address, broadcast address, subnet mask, MAC number, MTU, or other content). ifconf ifreq contained in the structure. The ifconf structures are often used to store all the information interfaces. for example: In the Linux system, the ifconfig command via ioctl interface to communicate with the kernel, e.g., when the system administrator to enter the following command to change the interface eth0 MTU size: ifconfig eth0 mtu 1250 First ifconfig command to open a socket, and initializes a data structure parameters of the system administrator through the input and transmits the data to the kernel via ioctl calls. SIOCSIFMTU is the command identifier. struct ifreq data; fd = socket (PF_INET, SOCK_DGRAM, 0); < ... initialize "data" .... 1882. err = ioctl (fd, SIOCSIFMTU, & data) ;, Read

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