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Chapter 16. ioctl Operations

Chapter 16. ioctl Operations. 16.1 Introduction. The ioctl function has traditionally been the system interface used for everything that didn’t fit into some other nicely defined category.

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Chapter 16. ioctl Operations

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  1. Chapter 16. ioctlOperations UNIX Network Programming

  2. 16.1 Introduction • The ioctl function has traditionally been the system interface used for everything that didn’t fit into some other nicely defined category. • Nevertheless numerous ioctls remain for implementation-dependent features related to network programming: obtaining the interface information, accessing the routing table, ARP cache • A common use of ioctl by network program ( typically server ) is to obtain information on all the host’s interfaces when the program starts : the interface addresses, whether the interface supports broadcasting, whether the interface supports multicasting, and so on. UNIX Network Programming

  3. 16.2 ioctl Function • The third argument is always a pointer, but the type of pointer depends on the request. • We can divide the requests related to networking into sex categories. • socket operations • file operations • interface operations • ARP cache operations • routing table operations • streams system #include <unistd.h> int ioctl ( int fd, int request, . . . /* void *arg */ ); Returns: 0 if OK, -1 on error UNIX Network Programming

  4. UNIX Network Programming

  5. 16.3 Socket Operations • SIOCATMASK • return through the integer pointed to by the third argument a nonzero value if the socket’s read pointer is currently at the out-of-band mark, of a zero value if the read pointer is not at the out-of-band mark. • SIOCGPGRP • return through the integer pointed to by the third argument either the process ID or the process group ID that is set to receive the SIGIO or SIGURG signal for this socket. • SIOCSPGRP • set either the process ID or the process group ID to receive the SIGIO or SIGURG signal for this socket from the integer pointed to by third argument. UNIX Network Programming

  6. 16.4 File Operations • FIONBIO • the nonblocking flag for the socket is cleared or turned on, depending whether the third argument to ioclt points to a zero or nonzero value, respectively. • FIOASYNC • the flag that governs the receipt of asynchronous I/O signals(SIGIO) for the socket is cleared or turned on, depending whether the third argument to ioctl points a zero or nonzero value, respectively. • FIONREAD • return in the integer pointed to by the third argument to ioctl the number of bytes currently in the socket receive buffer. • FIOSETOWN - Equivalent to SIOCSPGRP for a socket • FIOGETOWN - Equivalent to SIOCGPGRP for a socket UNIX Network Programming

  7. 16.5 Interface Configuration • From the kernel, get all the network interfaces configured on the system • In order to do it, use ioctl with SIOCGIFCONF • Before calling ioctl we allocate a buffer and an ifconf structure and the initialize the latter. UNIX Network Programming

  8. 16.5 Interface Configuration UNIX Network Programming

  9. 16.5 Interface Configuration struct ifconf { int ifc_len; /* Size of buffer. */ union { caddr_t ifcu_buf; struct ifreq *ifcu_req; } ifc_ifcu; }; #define ifc_buf ifc_ifcu.ifcu_buf /* Buffer address. */ #define ifc_req ifc_ifcu.ifcu_req /* Array of structures. */ #define IFNAMSIZ 16 struct ifreq { char ifrn_name[IFNAMSIZ]; /* Interface name, e.g. "en0". */ union { struct sockaddr ifru_addr; struct sockaddr ifru_dstaddr; struct sockaddr ifru_broadaddr; short int ifru_flags; int ifru_matric; caddr_t ifru_data; } ifr_ifru; }; #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_flags ifr_ifru.ifru_flags /* flags */ #define ifr_metric ifr_ifru.ifru_ivalue /* metric */ #define ifr_data ifr_ifru.ifru_data /* for use by interface */ UNIX Network Programming

  10. 16.6 get_cli_info function • Since many programs need to know all the interfaces on a system, we will develop a function of our own named get_ifi_info that returns a linked list of structures, one for each interface that is currently “up”. UNIX Network Programming

  11. Figure 16.5 unpifi.h header. #include "unp.h" #include <net/if.h> #define IFI_NAME 16 /* same as IFNAMSIZ in <net/if.h> */ #define IFI_HADDR 8 /* allow for 64-bit EUI-64 in future */ struct ifi_info { char ifi_name[IFI_NAME]; /* interface name, null terminated */ u_char ifi_haddr[IFI_HADDR]; /* hardware address */ u_short ifi_hlen; /* #bytes in hardware address: 0, 6, 8 */ short ifi_flags; /* IFF_xxx constants from <net/if.h> */ short ifi_myflags; /* our own IFI_xxx flags */ struct sockaddr *ifi_addr; /* primary address */ struct sockaddr *ifi_brdaddr; /* broadcast address */ struct sockaddr *ifi_dstaddr; /* destination address */ struct ifi_info *ifi_next; /* next of these structures */ }; #define IFI_ALIAS 1 /* ifi_addr is an alias */ /* function prototypes */ struct ifi_info *get_ifi_info(int, int); struct ifi_info *Get_ifi_info(int, int); void free_ifi_info(struct ifi_info *); UNIX Network Programming

  12. Figure 16.6 prifinfo program that calls our get_ifi_info function. (1/3) #include "unpifi.h" int main(int argc, char **argv) { struct ifi_info *ifi, *ifihead; struct sockaddr *sa; u_char *ptr; int i, family, doaliases; if (argc != 3) err_quit("usage: prifinfo <inet4|inet6> <doaliases>"); if (strcmp(argv[1], "inet4") == 0) family = AF_INET; #ifdef IPV6 else if (strcmp(argv[1], "inet6") == 0) family = AF_INET6; #endif else err_quit("invalid <address-family>"); doaliases = atoi(argv[2]); UNIX Network Programming

  13. Figure 16.6 prifinfo program that calls our get_ifi_info function. (2/3) for (ifihead = ifi = Get_ifi_info(family, doaliases); ifi != NULL; ifi = ifi->ifi_next) { printf("%s: <", ifi->ifi_name); if (ifi->ifi_flags & IFF_UP) printf("UP "); if (ifi->ifi_flags & IFF_BROADCAST) printf("BCAST "); if (ifi->ifi_flags & IFF_MULTICAST) printf("MCAST "); if (ifi->ifi_flags & IFF_LOOPBACK) printf("LOOP "); if (ifi->ifi_flags & IFF_POINTOPOINT) printf("P2P "); printf(">\n"); UNIX Network Programming

  14. Figure 16.6 prifinfo program that calls our get_ifi_info function. (3/3) if ( (i = ifi->ifi_hlen) > 0) { ptr = ifi->ifi_haddr; do { printf("%s%x", (i == ifi->ifi_hlen) ? " " : ":", *ptr++); } while (--i > 0); printf("\n"); } if ( (sa = ifi->ifi_addr) != NULL) printf(" IP addr: %s\n", Sock_ntop_host(sa, sizeof(*sa))); if ( (sa = ifi->ifi_brdaddr) != NULL) printf(" broadcast addr: %s\n", Sock_ntop_host(sa, sizeof(*sa))); if ( (sa = ifi->ifi_dstaddr) != NULL) printf(" destination addr: %s\n", Sock_ntop_host(sa, sizeof(*sa))); } free_ifi_info(ifihead); exit(0); } UNIX Network Programming

  15. lib/get_ifi_info.c (1/6) #include "unpifi.h" struct ifi_info * get_ifi_info(int family, int doaliases) { struct ifi_info *ifi, *ifihead, **ifipnext; int sockfd, len, lastlen, flags, myflags; char *ptr, *buf, lastname[IFNAMSIZ], *cptr; struct ifconf ifc; struct ifreq *ifr, ifrcopy; struct sockaddr_in *sinptr; sockfd = Socket(AF_INET, SOCK_DGRAM, 0); lastlen = 0; len = 100 * sizeof(struct ifreq); /* initial buffer size guess */ UNIX Network Programming

  16. lib/get_ifi_info.c (2/6) for ( ; ; ) { buf = Malloc(len); ifc.ifc_len = len; ifc.ifc_buf = buf; if (ioctl(sockfd, SIOCGIFCONF, &ifc) < 0) { if (errno != EINVAL || lastlen != 0) err_sys("ioctl error"); } else { if (ifc.ifc_len == lastlen) break; /* success, len has not changed */ lastlen = ifc.ifc_len; } len += 10 * sizeof(struct ifreq); /* increment */ free(buf); } ifihead = NULL; ifipnext = &ifihead; lastname[0] = 0; UNIX Network Programming

  17. lib/get_ifi_info.c (3/6) for (ptr = buf; ptr < buf + ifc.ifc_len; ) { ifr = (struct ifreq *) ptr; #ifdef HAVE_SOCKADDR_SA_LEN len = max(sizeof(struct sockaddr), ifr->ifr_addr.sa_len); #else switch (ifr->ifr_addr.sa_family) { #ifdef IPV6 case AF_INET6: len = sizeof(struct sockaddr_in6); break; #endif case AF_INET: default: len = sizeof(struct sockaddr); break; } #endif /* HAVE_SOCKADDR_SA_LEN */ ptr += sizeof(ifr->ifr_name) + len; /* for next one in buffer */ UNIX Network Programming

  18. lib/get_ifi_info.c (4/6) if (ifr->ifr_addr.sa_family != family) continue; /* ignore if not desired address family */ myflags = 0; if ( (cptr = strchr(ifr->ifr_name, ':')) != NULL) *cptr = 0; /* replace colon will null */ if (strncmp(lastname, ifr->ifr_name, IFNAMSIZ) == 0) { if (doaliases == 0) continue; /* already processed this interface */ myflags = IFI_ALIAS; } memcpy(lastname, ifr->ifr_name, IFNAMSIZ); ifrcopy = *ifr; Ioctl(sockfd, SIOCGIFFLAGS, &ifrcopy); flags = ifrcopy.ifr_flags; if ((flags & IFF_UP) == 0) continue; /* ignore if interface not up */ UNIX Network Programming

  19. lib/get_ifi_info.c (5/6) ifi = Calloc(1, sizeof(struct ifi_info)); *ifipnext = ifi; /* prev points to this new one */ ifipnext = &ifi->ifi_next; /* pointer to next one goes here */ ifi->ifi_flags = flags; /* IFF_xxx values */ ifi->ifi_myflags = myflags; /* IFI_xxx values */ memcpy(ifi->ifi_name, ifr->ifr_name, IFI_NAME); ifi->ifi_name[IFI_NAME-1] = '\0'; switch (ifr->ifr_addr.sa_family) { case AF_INET: sinptr = (struct sockaddr_in *) &ifr->ifr_addr; if (ifi->ifi_addr == NULL) { ifi->ifi_addr = Calloc(1, sizeof(struct sockaddr_in)); memcpy(ifi->ifi_addr, sinptr, sizeof(struct sockaddr_in)); UNIX Network Programming

  20. lib/get_ifi_info.c (6/6) #ifdef SIOCGIFBRDADDR if (flags & IFF_BROADCAST) { Ioctl(sockfd, SIOCGIFBRDADDR, &ifrcopy); sinptr = (struct sockaddr_in *) &ifrcopy.ifr_broadaddr; ifi->ifi_brdaddr = Calloc(1, sizeof(struct sockaddr_in)); memcpy(ifi->ifi_brdaddr, sinptr, sizeof(struct sockaddr_in)); } #endif #ifdef SIOCGIFDSTADDR if (flags & IFF_POINTOPOINT) { Ioctl(sockfd, SIOCGIFDSTADDR, &ifrcopy); sinptr = (struct sockaddr_in *) &ifrcopy.ifr_dstaddr; ifi->ifi_dstaddr = Calloc(1, sizeof(struct sockaddr_in)); memcpy(ifi->ifi_dstaddr, sinptr, sizeof(struct sockaddr_in)); } #endif } break; default: break; } } free(buf); return(ifihead); /* pointer to first structure in linked list */ } UNIX Network Programming

  21. Figure 16.10 free_ifi_info function: free dynamic memory allocated by get _ifi_info. void free_ifi_info(struct ifi_info *ifihead) { struct ifi_info *ifi, *ifinext; for (ifi = ifihead; ifi != NULL; ifi = ifinext) { if (ifi->ifi_addr != NULL) free(ifi->ifi_addr); if (ifi->ifi_brdaddr != NULL) free(ifi->ifi_brdaddr); if (ifi->ifi_dstaddr != NULL) free(ifi->ifi_dstaddr); ifinext = ifi->ifi_next; /* can't fetch ifi_next after free() */ free(ifi); /* the ifi_info{} itself */ } } UNIX Network Programming

  22. 16.7 Interface Operations • SIOCGIFADDR • return the unicast address in the ifr_addr member. • SIOCSIFADDR • sets the interface address from the ifr_addr member. • SIOCGIFFLAGS • return the interface flags in the ifr_flags member. • SIOCSIFFLAGS • sets the interface flags from the ifr_flags member. • SIOCGIFDSTADDR • return the point-to-point address in the ifr_dstaddr member. • SIOCSIFDSTADDR • set the point-to-point address from ifr_dstaddr member. UNIX Network Programming

  23. 16.7 Interface Operations • SIOCGIFBRDADDR • return the broadcast address in the ifr_broadaddr emember. • SIOCSIFBRDADDR • set the broadcast address from the ifr_boradaddr member. • SIOCGIFNETMASK • return the subnet mask in the ifr_addr member. • SIOCSIFNETMASK • set the subnet mask from the ifr_addr member. • SIOCGIFMETRIC • return the interface metric in the ifr_metric member. • SIOCSIFMETRIC • set the interface routing metric from the ifr_metric member. UNIX Network Programming

  24. 16.8 ARP Cache Operations struct arpreq { struct sockaddr arp_pa; /* protocol addesss */ struct sockaddr arp_ha; /* hardware address */ int arp_flags; /* flags */ }; #define ATF_INUSE 0x01 /* entry in use */ #define ATF_COM 0x02 /* completed entry (hardware addr valid) */ #define ATF_PERM 0x04 /* permanent entry */ #define ATF_PUBL 0x08 /* published entry (respond for other host) */ • SIOCSARP • add a new entry to the ARP cache or modify an existing entry. • SIOCDARP • delete an entry from the ARP cache. • SIOCGARP • get an entry from the ARP cache. UNIX Network Programming

  25. Figure 16.12 Print a host’s hardware addresses. int main(int argc, char **argv) { int family, sockfd; char str[INET6_ADDRSTRLEN]; char **pptr; unsigned char *ptr; struct arpreq arpreq; struct sockaddr_in *sin; pptr = my_addrs(&family); for ( ; *pptr != NULL; pptr++) { printf("%s: ", Inet_ntop(family, *pptr, str, sizeof(str))); switch (family) { case AF_INET: sockfd = Socket(AF_INET, SOCK_DGRAM, 0); sin = (struct sockaddr_in *) &arpreq.arp_pa; bzero(sin, sizeof(struct sockaddr_in)); sin->sin_family = AF_INET; memcpy(&sin->sin_addr, *pptr, sizeof(struct in_addr)); Ioctl(sockfd, SIOCGARP, &arpreq); ptr = &arpreq.arp_ha.sa_data[0]; printf("%x:%x:%x:%x:%x:%x\n", *ptr, *(ptr+1), *(ptr+2), *(ptr+3), *(ptr+4), *(ptr+5)); break; default: err_quit("unsupported address family: %d", family); } } exit(0); } UNIX Network Programming

  26. 16.9 Routing Table Operations • Two ioctl requests are provided to operate on the routing table. • These two requests require that the third argument to ioctl be a pointer to an rtentry structure,which is defined by including the <net/route.h> header. • Only the superuser can issue these requests. • SIOCADDRT - add an entry to the routing table. • SIOCDELRT - delete an entry to the routing table. UNIX Network Programming

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