Chapter 16.

ioctl Operations

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16.1 IntroductionThe ioctl function has traditionally been the system interface used for everything that didnt 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 cacheA common use of ioctl by network program ( typically server ) is to obtain information on all the hosts interfaces when the program starts : the interface addresses, whether the interface supports broadcasting, whether the interface supports multicasting, and so on.

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16.2 ioctl FunctionThe 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 operationsfile operationsinterface operationsARP cache operationsrouting table operationsstreams system#include int ioctl ( int fd, int request, . . . /* void *arg */ );Returns: 0 if OK, -1 on error

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16.3 Socket OperationsSIOCATMASKreturn through the integer pointed to by the third argument a nonzero value if the sockets 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.

SIOCGPGRPreturn 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.

SIOCSPGRPset 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.

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16.4 File OperationsFIONBIOthe 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.FIOASYNCthe 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.FIONREADreturn 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 socketFIOGETOWN - Equivalent to SIOCGPGRP for a socket

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16.5 Interface ConfigurationFrom the kernel, get all the network interfaces configured on the systemIn order to do it, use ioctl with SIOCGIFCONFBefore calling ioctl we allocate a buffer and an ifconf structure and the initialize the latter.

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16.5 Interface Configuration

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16.5 Interface Configurationstruct 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 IFNAMSIZ16struct 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 */

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16.6 get_cli_info functionSince 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.

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Figure 16.5 unpifi.h header.#include"unp.h"#include

#defineIFI_NAME16/* same as IFNAMSIZ in */#defineIFI_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 */ 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 */};#defineIFI_ALIAS1/* 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 *);

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Figure 16.6 prifinfo program that calls our get_ifi_info function. (1/3)#include"unpifi.h"

intmain(int argc, char **argv){struct ifi_info*ifi, *ifihead;struct sockaddr*sa;u_char*ptr;inti, family, doaliases;

if (argc != 3)err_quit("usage: prifinfo ");

if (strcmp(argv[1], "inet4") == 0)family = AF_INET;#ifdefIPV6else if (strcmp(argv[1], "inet6") == 0)family = AF_INET6;#endifelseerr_quit("invalid ");doaliases = atoi(argv[2]);

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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: \n");

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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);}

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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;intsockfd, len, lastlen, flags, myflags;char*ptr, *buf, lastname[IFNAMSIZ], *cptr;struct ifconfifc;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 */

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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;

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lib/get_ifi_info.c (3/6)for (ptr = buf; ptr < buf + ifc.ifc_len; ) {ifr = (struct ifreq *) ptr;

#ifdefHAVE_SOCKADDR_SA_LENlen = max(sizeof(struct sockaddr), ifr->ifr_addr.sa_len);#elseswitch (ifr->ifr_addr.sa_family) {#ifdefIPV6case AF_INET6:len = sizeof(struct sockaddr_in6);break;#endifcase AF_INET:default:len = sizeof(struct sockaddr);break;}#endif/* HAVE_SOCKADDR_SA_LEN */ptr += sizeof(ifr->ifr_name) + len;/* for next one in buffer */

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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 */

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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));

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lib/get_ifi_info.c (6/6)#ifdefSIOCGIFBRDADDRif (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

#ifdefSIOCGIFDSTADDRif (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 */}

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Figure 16.10 free_ifi_info function: free dynamic memory allocated by get _ifi_info.voidfree_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 */}}

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16.7 Interface OperationsSIOCGIFADDR return the unicast address in the ifr_addr member.SIOCSIFADDRsets the interface address from the ifr_addr member.SIOCGIFFLAGSreturn the interface flags in the ifr_flags member.SIOCSIFFLAGSsets the interface flags from the ifr_flags member.SIOCGIFDSTADDRreturn the point-to-point address in the ifr_dstaddr member.SIOCSIFDSTADDRset the point-to-point address from ifr_dstaddr member.

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16.7 Interface OperationsSIOCGIFBRDADDRreturn the broadcast address in the ifr_broadaddr emember.SIOCSIFBRDADDRset the broadcast address from the ifr_boradaddr member.SIOCGIFNETMASKreturn the subnet mask in the ifr_addr member.SIOCSIFNETMASKset the subnet mask from the ifr_addr member.SIOCGIFMETRICreturn the interface metric in the ifr_metric member.SIOCSIFMETRICset the interface routing metric from the ifr_metric member.

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16.8 ARP Cache OperationsSIOCSARPadd a new entry to the ARP cache or modify an existing entry.SIOCDARPdelete an entry from the ARP cache.SIOCGARPget an entry from the ARP cache.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) */

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Figure 16.12 Print a hosts hardware addresses.int main(int argc, char **argv){intfamily, sockfd;charstr[INET6_ADDRSTRLEN];char**pptr;unsigned char*ptr;struct arpreqarpreq;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); }

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16.9 Routing Table OperationsTwo 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 header.Only the superuser can issue these requests.

SIOCADDRT - add an entry to the routing table.SIOCDELRT - delete an entry to the routing table.

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