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, 14 insertions, 1 deletions

diff --git a/pcap-pf.c b/pcap-pf.c
index 0d7a9eb7..33bb7b7c 100644
--- a/pcap-pf.c
+++ b/pcap-pf.c
@@ -321,6 +321,9 @@ pcap_activate_pf(pcap_t *p)
 	 * its argument, even though it takes a "char *" rather than a
 	 * "const char *" as its first argument.  That appears to be
 	 * the case, at least on Digital UNIX 4.0.
+	 *
+	 * XXX - is there an error that means "no such device"?  Is
+	 * there one that means "that device doesn't support pf"?
 	 */
 	p->fd = pfopen(p->opt.source, O_RDWR);
 	if (p->fd == -1 && errno == EACCES)
@@ -515,10 +518,20 @@ pcap_create_interface(const char *device, char *ebuf)
 	return (p);
 }
 
+/*
+ * XXX - is there an error from pfopen() that means "no such device"?
+ * Is there one that means "that device doesn't support pf"?
+ */
+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));
 }
 
 static int