Let the platform decide how to check capturable interfaces.

(Git's annoying policy of expecting a short one-line description of every
change means that the first line isn't very explanatory.)

Make pcap_findalldevs_interfaces() take as an argument a function that's
used to check whether an interface can be captured on or not, rather
than doing the check by trying to open the device for capturing.

This lets pcap_findalldevs() find interfaces even if you don't have
permission to capture on them; that way, instead of users saying "why
isn't {tcpdump -D, tshark -D, dumpcap -D, Wireshark, etc.} showing me
any interfaces?", they'll say "why am I getting a 'you don't have
permissions' error when I try to capture on this interface?", which is a
better description of the underlying problem.

On some platforms, it also avoids a bunch of extra work when getting a
list of interfaces.

1 files changed, 18 insertions, 1 deletions

diff --git a/pcap-nit.c b/pcap-nit.c
index db1be00c..2aa84ba4 100644
--- a/pcap-nit.c
+++ b/pcap-nit.c
@@ -288,6 +288,13 @@ pcap_activate_nit(pcap_t *p)
 	(void)strncpy(snit.snit_ifname, p->opt.source, NITIFSIZ);
 
 	if (bind(fd, (struct sockaddr *)&snit, sizeof(snit))) {
+		/*
+		 * XXX - there's probably a particular bind error that
+		 * means "there's no such device" and a particular bind
+		 * error that means "that device doesn't support NIT";
+		 * they might be the same error, if they both end up
+		 * meaning "NIT doesn't know about that device".
+		 */
 		pcap_snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
 		    "bind: %s: %s", snit.snit_ifname, pcap_strerror(errno));
 		goto bad;
@@ -360,8 +367,18 @@ pcap_create_interface(const char *device, char *ebuf)
 	return (p);
 }
 
+/*
+ * XXX - there's probably a particular bind error that means "that device
+ * doesn't support NIT"; if so, we should try a bind and use that.
+ */
+static int
+can_be_bound(const char *name _U_)
+{
+	return (1);
+}
+
 int
 pcap_platform_finddevs(pcap_if_t **alldevsp, char *errbuf)
 {
-	return (pcap_findalldevs_interfaces(alldevsp, errbuf));
+	return (pcap_findalldevs_interfaces(alldevsp, errbuf, can_be_bound));
 }