set the snaplen to max(snaplen, mtu). From Guy Harris
<gharris@flashcom.net>
diff --git a/pcap-snoop.c b/pcap-snoop.c
index d756864..eedbf99 100644
--- a/pcap-snoop.c
+++ b/pcap-snoop.c
@@ -20,7 +20,7 @@
*/
#ifndef lint
static const char rcsid[] =
- "@(#) $Header: /tcpdump/master/libpcap/pcap-snoop.c,v 1.23 2000-04-27 14:24:13 itojun Exp $ (LBL)";
+ "@(#) $Header: /tcpdump/master/libpcap/pcap-snoop.c,v 1.24 2000-04-29 10:09:23 assar Exp $ (LBL)";
#endif
#include <sys/param.h>
@@ -128,7 +128,10 @@
struct sockaddr_raw sr;
struct snoopfilter sf;
u_int v;
+ int ll_hdrlen;
+ int snooplen;
pcap_t *p;
+ struct ifreq ifr;
p = (pcap_t *)malloc(sizeof(*p));
if (p == NULL) {
@@ -160,18 +163,6 @@
}
v = 64 * 1024;
(void)setsockopt(fd, SOL_SOCKET, SO_RCVBUF, (char *)&v, sizeof(v));
- if (ioctl(fd, SIOCSNOOPLEN, &snaplen) < 0) {
- snprintf(ebuf, PCAP_ERRBUF_SIZE, "SIOCSNOOPLEN: %s",
- pcap_strerror(errno));
- goto bad;
- }
- p->snapshot = snaplen;
- v = 1;
- if (ioctl(fd, SIOCSNOOPING, &v) < 0) {
- snprintf(ebuf, PCAP_ERRBUF_SIZE, "SIOCSNOOPING: %s",
- pcap_strerror(errno));
- goto bad;
- }
/*
* XXX hack - map device name to link layer type
*/
@@ -188,18 +179,73 @@
strncmp("el", device, 2) == 0) {
p->linktype = DLT_EN10MB;
p->offset = RAW_HDRPAD(sizeof(struct ether_header));
+ ll_hdrlen = sizeof(struct ether_header);
} else if (strncmp("ipg", device, 3) == 0 ||
strncmp("rns", device, 3) == 0 || /* O2/200/2000 FDDI */
strncmp("xpi", device, 3) == 0) {
p->linktype = DLT_FDDI;
p->offset = 3; /* XXX yeah? */
+ ll_hdrlen = 13;
} else if (strncmp("ppp", device, 3) == 0) {
p->linktype = DLT_RAW;
+ ll_hdrlen = 0; /* DLT_RAW meaning "no PPP header, just the IP packet"? */
} else if (strncmp("lo", device, 2) == 0) {
p->linktype = DLT_NULL;
+ ll_hdrlen = 4; /* is this just like BSD's loopback device? */
} else {
snprintf(ebuf, PCAP_ERRBUF_SIZE,
"snoop: unknown physical layer type");
+ goto bad;
+ }
+ #ifdef SIOCGIFMTU
+ /*
+ * XXX - IRIX appears to give you an error if you try to set the
+ * capture length to be greater than the MTU, so let's try to get
+ * the MTU first and, if that succeeds, trim the snap length
+ * to be no greater than the MTU.
+ */
+ (void)strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));
+ if (ioctl(fd, SIOCGIFMTU, (char *)&ifr) < 0) {
+ sprintf(ebuf, "SIOCGIFMTU: %s", pcap_strerror(errno));
+ goto bad;
+ }
+ /*
+ * OK, we got it.
+ *
+ * XXX - some versions of IRIX 6.5 define "ifr_mtu" and have an
+ * "ifru_metric" member of the "ifr_ifru" union in an "ifreq"
+ * structure, others don't.
+ *
+ * I've no idea what's going on, so, if "ifr_mtu" isn't defined,
+ * we define it as "ifr_metric", as using that field appears to
+ * work on the versions that lack "ifr_mtu" (and, on those that
+ * don't lack it, "ifru_metric" and "ifru_mtu" are both "int"
+ * members of the "ifr_ifru" union, which suggests that they
+ * may be interchangeable in this case).
+ */
+ #ifndef ifr_mtu
+ #define ifr_mtu ifr_metric
+ #endif
+ if (snaplen > ifr.ifr_mtu)
+ snaplen = ifr.ifr_mtu;
+ #endif
+
+ /*
+ * The argument to SIOCSNOOPLEN is the number of link-layer
+ * payload bytes to capture - it doesn't count link-layer
+ * header bytes.
+ */
+ snooplen = snaplen - ll_hdrlen;
+ if (snooplen < 0)
+ snooplen = 0;
+ if (ioctl(fd, SIOCSNOOPLEN, &snooplen) < 0) {
+ sprintf(ebuf, "SIOCSNOOPLEN: %s", pcap_strerror(errno));
+ goto bad;
+ }
+ p->snapshot = snaplen;
+ v = 1;
+ if (ioctl(fd, SIOCSNOOPING, &v) < 0) {
+ sprintf(ebuf, "SIOCSNOOPING: %s", pcap_strerror(errno));
goto bad;
}
