From: Guy Harris <guy@alum.mit.edu>
Date: Mon, 12 Oct 2009 23:24:57 +0000 (-0700)
Subject: In pcap_read_linux_mmap(), if there are no frames available, call poll()
X-Git-Tag: libpcap-1.1.0~67
X-Git-Url: https://git.tcpdump.org/libpcap/commitdiff_plain/bf7491046a6123f40be6993a24a61e9525a44666

In pcap_read_linux_mmap(), if there are no frames available, call poll()
even if we're in non-blocking mode, to pick up any error indications -
in that case, use a timeout of 0, so poll() doesn't block.

Don't test individual exceptional-condition bits in the poll() return
unless one of them is set, so we just do one test in the typical (no
exceptional condition) case.
---

diff --git a/pcap-linux.c b/pcap-linux.c
index 8356ba54..48cad3aa 100644
--- a/pcap-linux.c
+++ b/pcap-linux.c
@@ -2929,42 +2929,47 @@ pcap_get_ring_frame(pcap_t *handle, int status)
 	return h.raw;
 }
 
+#ifndef POLLRDHUP
+#define POLLRDHUP 0
+#endif
+
 static int
 pcap_read_linux_mmap(pcap_t *handle, int max_packets, pcap_handler callback, 
 		u_char *user)
 {
+	int timeout;
 	int pkts = 0;
 	char c;
 
 	/* wait for frames availability.*/
-	if ((handle->md.timeout >= 0) &&
-	    !pcap_get_ring_frame(handle, TP_STATUS_USER)) {
+	if (!pcap_get_ring_frame(handle, TP_STATUS_USER)) {
 		struct pollfd pollinfo;
 		int ret;
 
 		pollinfo.fd = handle->fd;
 		pollinfo.events = POLLIN;
 
+		if (handle->md.timeout == 0)
+			timeout = -1;	/* block forever */
+		else if (handle->md.timeout > 0)
+			timeout = handle->md.timeout;	/* block for that amount of time */
+		else
+			timeout = 0;	/* non-blocking mode - poll to pick up errors */
 		do {
-			/* poll() requires a negative timeout to wait forever */
-			ret = poll(&pollinfo, 1, (handle->md.timeout > 0)?
-			 			handle->md.timeout: -1);
-			if ((ret < 0) && (errno != EINTR)) {
+			ret = poll(&pollinfo, 1, timeout);
+			if (ret < 0 && errno != EINTR) {
 				snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, 
 					"can't poll on packet socket: %s",
 					pcap_strerror(errno));
 				return PCAP_ERROR;
-			} else if (ret > 0) {
+			} else if (ret > 0 &&
+			    (pollinfo.revents & (POLLHUP|POLLRDHUP|POLLERR|POLLNVAL))) {
 				/*
-				 * There's some indication on the descriptor.
-				 * Check for indications other than
-				 * "you can read on this descriptor".
+				 * There's some indication other than
+				 * "you can read on this descriptor" on
+				 * the descriptor.
 				 */
-#ifdef POLLRDHUP
 				if (pollinfo.revents & (POLLHUP | POLLRDHUP)) {
-#else
-				if (pollinfo.revents & POLLHUP) {
-#endif
 					snprintf(handle->errbuf,
 						PCAP_ERRBUF_SIZE,
 						"Hangup on packet socket");