Handle a timeout value of 0 better with TPACKET_V3.

If the user specified a timeout value of 0, and we don't have any
packets to return from pcap_read_linux_mmap_v3(), go back and wait for
packets.  Yes, this means waiting indefinitely, but that's what the
documentation used to say, and what we're making it say again; if this
is a problem, *don't use a timeout value of 0*.

This should fix GitHub libpcap issue #350.

3 files changed, 14 insertions, 9 deletions

diff --git a/pcap-linux.c b/pcap-linux.c
index 38df97b5..9ff71ee9 100644
--- a/pcap-linux.c
+++ b/pcap-linux.c
@@ -4474,6 +4474,7 @@ pcap_read_linux_mmap_v3(pcap_t *handle, int max_packets, pcap_handler callback,
 	int pkts = 0;
 	int ret;
 
+again:
 	if (handlep->current_packet == NULL) {
 		/* wait for frames availability.*/
 		ret = pcap_wait_for_frames_mmap(handle);
@@ -4482,8 +4483,13 @@ pcap_read_linux_mmap_v3(pcap_t *handle, int max_packets, pcap_handler callback,
 		}
 	}
 	h.raw = pcap_get_ring_frame(handle, TP_STATUS_USER);
-	if (!h.raw)
+	if (!h.raw) {
+		if (pkts == 0 && handlep->timeout == 0) {
+			/* Block until we see a packet. */
+			goto again;
+		}
 		return pkts;
+	}
 
 	/* non-positive values of max_packets are used to require all
 	 * packets currently available in the ring */
@@ -4564,6 +4570,10 @@ pcap_read_linux_mmap_v3(pcap_t *handle, int max_packets, pcap_handler callback,
 			return PCAP_ERROR_BREAK;
 		}
 	}
+	if (pkts == 0 && handlep->timeout == 0) {
+		/* Block until we see a packet. */
+		goto again;
+	}
 	return pkts;
 }
 #endif /* HAVE_TPACKET3 */
diff --git a/pcap.3pcap.in b/pcap.3pcap.in
index 03afb992..d3c01692 100644
--- a/pcap.3pcap.in
+++ b/pcap.3pcap.in
@@ -172,11 +172,9 @@ arbitrarily long period of time.
 .IP
 Not all platforms support a read timeout; on platforms that
 don't, the read timeout is ignored.  A zero value for the timeout,
-on platforms that support a read timeout, has platform-dependent
-behavior that could cause a read to wait for an unlimited amount
-of time until the capture buffer fills up or could cause a read timeout
-of 1 millisecond to be used.  We recommend that a value of zero not be
-used.
+on platforms that support a read timeout,
+will cause a read to wait forever to allow enough packets to
+arrive, with no timeout.
 .IP
 .BR NOTE :
 the read timeout cannot be used to cause calls that read
diff --git a/pcap_set_timeout.3pcap b/pcap_set_timeout.3pcap
index fa3b167e..1a0641ee 100644
--- a/pcap_set_timeout.3pcap
+++ b/pcap_set_timeout.3pcap
@@ -36,9 +36,6 @@ sets the read timeout that will be used on a capture handle when
 the handle is activated to
 .IR to_ms ,
 which is in units of milliseconds.
-.LP
-The behavior, if the timeout isn't specified, is undefined.  We
-recommend always setting the timeout to a non-zero value.
 .SH RETURN VALUE
 .B pcap_set_timeout()
 returns 0 on success or