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ioctl Operations

Computer Network Programming

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Use of ioctl()

• It is the system interface to set and get attributes of

• devices, sockets, files, • interfaces • tables like routing table, arp table...

• The same operations can be performed by • Use of special functions such as tcgetattr()• Use of routing domain sockets (AF_ROUTE family)• Use of fcntl function

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ioctl function()#include <unistd.h>int ioctl (int fd, int request, void *arg);

arg pointer type depends on the request.

Request can be divided into following categories:- Socket operations- File operations- Interface operations- ARP cache operations- Routing table operations

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Socket Operations

– SIOCATMARK: integer• Return if the socket’s read pointer is currently on

the out-of-band data

– SIOCGPGRP: int• Return the process ID or the process group ID that is

set to receive the SIGIO or SIGURG signal for this socket

– SIOCSPGRP: int• Set either the process ID or process group ID to

receive the SIGIO or SIGURG signal for this socket

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File Operations

– FIONBIO: integer– Clear or turn on the non-blocking flag for the socket.

– FIOASYNC: integer– Clear or turn on the receipt of asynchronous I/O signals

(SIGIO) for the socket.

– FIONREAD: integer– Return the number of bytes currently available in the

socket receive buffer.

– FIOSETOWN; integer– Equivalent to SIOCSPGRP for a socket

– FIOGETOWN: integer– Equivalent to SIOCGPGRP for a socket

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Interface Configuration

– It is possible to obtain information about all the network interfaces configured on the system

– IP address, flags <BCAST, PTP, MCAST, ...>, Bcast address, Interface name, ....

– It is possible to set the IP address, bcast address, dest address for ptp links, some flags for the interface

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Interface OperationsREQUEST Description Datatype-----------------------------------------------------------------------------------------SIOCGIFCONF get list of all interfaces struct ifconfSIOCSIFADDR set interface address struct ifreqSIOCGIFADDR get interface address struct ifreqSIOCSIFFLAGS set interface flags struct ifreqSIOCGIFFLAGS get interface flags struct ifreqSIOCSIFDSTADDR set point-to-point address struct ifreqSIOCGIFDSTADDR get point-to-point address struct ifreqSIOCSIFBRADDR set broadcast address struct ifreqSIOCGIFBRADDR get broadcast address struct ifreqSIOCGIFNETMASK get subnet mask struct ifreqSIOCSIFNETMASK set subnet mask struct ifreqSIOCGIFMETRIC get interface metric struct ifreqSIOCSIFMETRIC set interface metric struct ifreq

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ifconf and ifreq structures

struct ifconf {int ifc_len; /* size of associated 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 returned */};

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struct ifreq {#define IFNAMSIZ 16

char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */union {

struct sockaddr ifru_addr; /* size = 16 bytes */struct sockaddr ifru_dstaddr;char ifru_oname[IFNAMSIZ]; /* other if name */struct sockaddr ifru_broadaddr;int ifru_index; /* interface index */short ifru_flags;int ifru_metric;char ifru_data[1]; /* interface dependent data */char ifru_enaddr[6];int if_muxid[2]; /* mux id's for arp and ip *

} ifr_ifru;#define ifr_addr ifr_ifru.ifru_addr /* address */#define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */#define ifr_oname ifr_ifru.ifru_oname /* other if name */#define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */#define ifr_flags ifr_ifru.ifru_flags /* flags */#define ifr_metric ifr_ifru.ifru_metric /* metric */#define ifr_data ifr_ifru.ifru_data /* for use by interface */#define ifr_enaddr ifr_ifru.ifru_enaddr /* ethernet address */#define ifr_index ifr_ifru.ifru_index /* interface index */};

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Getting Interface list

• get_ifi_info() function• Will return the list of interface information • Each list entry is a structure of type struct ifi_info

• Will call ioctl() with request type SIOCGIFCONF to get the list

– This call will return a an array of ifreq structures: each structure will include info about the interface

• For each returned ifreq structure about an interface, it can get more information by calling ioctl again with a different request type

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ifi_info structure

#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 */};

get_ifi_info() returns the list of the following structure:

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Use of get_ifi_info Functionint 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 IPV6else if (strcmp(argv[1], "inet6") == 0)

family = AF_INET6;#endif

elseerr_quit("invalid <address-family>");

doaliases = atoi(argv[2]);

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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");

if ( (i = ifi->ifi_hlen) > 0) {ptr = ifi->ifi_haddr;do {

printf("%s%x", (i == ifi->ifi_hlen) ? " " : ":", *ptr++);} while (--i > 0);printf("\n");

}

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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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Example Run

aspendos{korpe}:> prifinfo inet4 doaliaseslo0: <UP MCAST LOOP > IP addr: 127.0.0.1le0: <UP BCAST MCAST > IP addr: 139.179.21.217 broadcast addr: 139.179.21.255

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Implementation of get_ifi_info() Functionstruct 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 */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);

} /* continued on the next page */

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ifihead = NULL;ifipnext = &ifihead;lastname[0] = 0;

/* end get_ifi_info1 */

/* include get_ifi_info2 */for (ptr = buf; ptr < buf + ifc.ifc_len; ) {

ifr = (struct ifreq *) ptr;

len = max(sizeof(struct sockaddr), ifr->ifr_addr.sa_len);

switch (ifr->ifr_addr.sa_family) {case AF_INET6:

len = sizeof(struct sockaddr_in6);break;

case AF_INET:default:

len = sizeof(struct sockaddr);break;

}ptr += sizeof(ifr->ifr_name) + len; /* for next one in buffer */

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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 */

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 */

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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';

/* end get_ifi_info2 *//* include get_ifi_info3 */

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));

#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

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#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 */

}/* end get_ifi_info */

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ARP Cache Operations

REQUEST Description Data TypeSIOCSARP add a new entry to arp cache struct arpreqSIOCDARP delete an entry from arp cache struct arpreqSIOCGARP get an entry from arp cache struct arpreq

struct arpreq {struct sockaddr arp_pa; struct sockaddr arp_flags; int arp_flags;

}

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Routing Table Operations

REQUEST Description Data TypeSIOCADDRT add an entry to the routing table struct rtentrySIOCDELRT delete an entry from routing table struct rtentry

struct rtentry defined in <net/route.h>

You have to be “root” in order to add and delete routing table entry.

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/dev/kmem and sysctl()

• There is no ioctl request type for getting the ARP and Routing table entry list.

• The list can be obtained by reading the kernel’s memory by opening /dev/kmem and reading from it.

• Or you can use the sysctl() function.