Re: consistent ioctl for getting all net interfaces?

[Tigran Aivazian]

I forgot to mention that I tested on some early 2.6 (pre) and it worked
fine. If SIOCGIFCONF was broken in the more recent 2.6 kernels then I
should re-test and revisit this function...

Kind regards
Tigran

On Sun, 23 May 2004, Tigran Aivazian wrote:

> On Sat, 22 May 2004, Joshua Kwan wrote:
> > I'm interested in not having to parse /proc/net/dev to get a list of all
> > available (not necessarily even up) interfaces on the system. I
> > investigated the ioctl SIOCGIFCONF, but it seems to behave differently on
> > 2.4 and 2.6 series kernels, e.g. sometimes it won't return all interfaces.
> > 
> > Is there some end-all ioctl that does what I want, or am I forever doomed
> > to process /proc/net/dev (in C, no less..)?
> > 
> > Please CC me on replies, I don't read this list very often any more.
> 
> Of course this is possible and here is the solution I wrote some time ago
> (ioctl-based).
> 
> Note that a more simple solution is also possible but is less portable
> (because will depend on glibc version).
> 
> /* TCPCAP endpoint, just an opaque handle for applications */
> struct tcpcap {
>         int fd;                         /* socket file descriptor */
>         struct timeval *ts;             /* user supplied addr of timestamp */
>         struct sockaddr_ll *from;       /* user supplied addr of extra info */
>         int nports;                     /* number of bits set in ->ports */
>         int maxport;                    /* highest port number set in ->ports */
>         unsigned char *ports;           /* ports currently set in ->lsf */
>         unsigned char *setports;        /* pending ports to be added */
>         unsigned char *clrports;        /* pending ports to be removed */
>         int recv_buflen;                /* socket receive buffer size */
>         struct sock_fprog *lsf;         /* compiled filter program */
>         struct sock_filter *lsf_insns;  /* the actual LSF instructions */
>         int snaplen;                    /* length of part of each packet */
>         int pkt_count;                  /* number of packets seen */
>         int promisc;                    /* set interface(s) to promisc. mode */
>         struct tcpcap_if *iface;        /* list of network interfaces */
>         int ifcount;                    /* number of elements in ->iface[] */
> };
> 
> 
> /* 
>  * internal helper: get the list of all IPv4 up interfaces
>  * and record their name and IP address into pcap->iface[]
>  * array. Also set promiscuous mode as requested via pcap->promisc.
>  */
> static int walkiflist(struct tcpcap *pcap)
> {
> 	struct ifconf ifc;
> 	struct ifreq *ifreqs, *ifr;
> 	int fd, rq_len, nifs, i, ret = 0;
> 
> 	/* this is a helper datagram socket which we must create
> 	 * because the actual packet socket is created later on,
> 	 * at tcpcap_start() time.
> 	 */
> 	fd = socket(PF_INET, SOCK_DGRAM, 0);
> 	if (fd < 0) {
> 		DPRINTF("socket(), errno=%d (%s)\n",
> 				errno, strerror(errno));
> 		return TERR_SOCKET;
> 	}
> 
> 	ifc.ifc_buf = NULL;
> 	rq_len = 4*sizeof(struct ifreq);
> 	do {
> 		ifc.ifc_len = rq_len;
> 		ifc.ifc_buf = realloc(ifc.ifc_buf, ifc.ifc_len);
> 		if (ifc.ifc_buf == NULL) {
> 			DPRINTF("ifc.buf = realloc() failed\n");
> 			ret = TERR_REALLOC;
> 			goto outclose;
> 		}
> 		if(ioctl(fd, SIOCGIFCONF, &ifc) < 0) {
> 			DPRINTF("ioctl(SIOCGIFCONF), errno=%d (%s)\n",
> 					errno, strerror(errno));
> 			if (ifc.ifc_buf)
> 				free(ifc.ifc_buf);
> 			ret = TERR_IOCTL;
> 			goto outclose;
> 		}
> 		rq_len *= 2;
> 	} while (rq_len < sizeof(struct ifreq) + ifc.ifc_len);
> 
> 	nifs = ifc.ifc_len / sizeof(struct ifreq);
> 	ifreqs = realloc(ifc.ifc_buf, nifs*sizeof(struct ifreq));
> 	if (ifreqs == NULL) {
> 		DPRINTF("ifreqs = realloc()\n");
> 		ret = TERR_REALLOC;
> 		free(ifc.ifc_buf);
> 		goto outclose;
> 	}
> 
> 	/* allocate enough space for the maximum number of interfaces */
> 	pcap->iface = zalloc(nifs*sizeof(struct tcpcap_if));
> 	if (pcap->iface == NULL) {
> 		DPRINTF("pcap->iface = zalloc() failed\n");
> 		ret = TERR_ZALLOC;
> 		goto outfree;
> 	}
> 
> 	/* look through what we found and select only the 'interesting' ones */
> 	for (ifr = ifreqs, i=0; i<nifs; ifr++, i++) {
> 		struct sockaddr_in *addr;
> 
> 		/* only interested in IPv4 */
> 		if (ifr->ifr_addr.sa_family != AF_INET)
> 			continue;
> 
> 		/* not interested in loopback */
> 		if (!strncmp(ifr->ifr_name, "lo", 2))
> 			continue;
> 
> 		/* request flags because SIOCGIFCONF only 
> 		 * initialized name, family and address
> 		 */
> 		if(ioctl(fd, SIOCGIFFLAGS, ifr) < 0) {
> 			DPRINTF("ioctl(SIOCGIFFLAGS), errno=%d (%s)\n",
> 					errno, strerror(errno));
> 			ret = TERR_IOCTL;
> 			goto outfree;
> 		}
> 
> 		/* not interested in down interfaces */
> 		if (!(ifr->ifr_flags & IFF_UP))
> 			continue;
> 
> 		/* OK, this interface passed all our criteria, so
> 		 * record it into pcap->iface[] array
> 		 */
> 		pcap->iface[pcap->ifcount].ifname =strdup(ifr->ifr_name);
> 		addr = (struct sockaddr_in *)&(ifr->ifr_addr);
> 		pcap->iface[pcap->ifcount].addr = htonl(addr->sin_addr.s_addr);
> 
> 		/* if required set this interface into promisc. mode,
> 		 * unless it is already in promiscuous mode.
> 		 */
> 		if (pcap->promisc && !(ifr->ifr_flags & IFF_PROMISC)) {
> 
> 			/* enable promiscuous mode */
> 			ifr->ifr_flags |= IFF_PROMISC;
> 
> 			/* set interface flags */
> 			if (ioctl(fd, SIOCSIFFLAGS, ifr) == -1) {
> 				DPRINTF("ioctl(SIOCSIFFLAGS), errno=%d (%s)\n", 
> 					errno, strerror(errno));
> 				ret = TERR_IOCTL;
> 				goto outfree;
> 			}
> 
> 			/* record the fact that we modified this interface */
> 			pcap->iface[pcap->ifcount].promisc = 1;
> 			DPRINTF("Enabled promisc. mode on %s (0x%x)\n", 
> 					pcap->iface[pcap->ifcount].ifname,
> 					pcap->iface[pcap->ifcount].addr);
> 		}
> 
> 		pcap->ifcount++;
> 	}
> 
> outfree:
> 	free(ifreqs);
> 
> outclose:
> 	close(fd);
> 
> 	return ret;
> }
> 
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