pcap_set_fanout_linux: use a proper flag to enable

Hacking around int to assume values lower than 0 will disable fanout is risky. int size is platform dependent assuming its size is risky.
the-tcpdump-group · Apr 16, 2020 · 929be78 · 929be78
1 parent a8f5ee2
commit 929be78
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Showing 5 changed files with 16 additions and 16 deletions.
diff --git a/pcap-int.h b/pcap-int.h
@@ -125,7 +125,8 @@ struct pcap_opt {
 	 */
 #ifdef __linux__
 	int	protocol;	/* protocol to use when creating PF_PACKET socket */
-	int	fanout;		/* If >= 0 - fanout is enabled. 16 lower bits are the group id; upper bits are the mode. */
+	int	fanout_enabled;	/* If evaluates to TRUE, fanout mode is enabled; default: FALSE. */
+	int	fanout_opt;	/* 16 lower bits are the group id; upper bits are the mode. */
 #endif
 #ifdef _WIN32
 	int	nocapture_local;/* disable NPF loopback */

diff --git a/pcap-linux.c b/pcap-linux.c
@@ -3734,8 +3734,8 @@ activate_sock(pcap_t *handle, int is_any_device)
 	 * Add the packet socket into FANOUT group, if needed.
 	 */
 #ifdef PACKET_FANOUT
-	if (handle->opt.fanout > 0) {
-		val = handle->opt.fanout;
+	if (handle->opt.fanout_enabled) {
+		val = handle->opt.fanout_opt;
 		if (setsockopt(sock_fd, SOL_PACKET, PACKET_FANOUT,
 		               &val, sizeof(val)) < 0) {
 			pcap_fmt_errmsg_for_errno(handle->errbuf,
@@ -7152,18 +7152,15 @@ pcap_set_protocol_linux(pcap_t *p, int protocol)
 }
 
 int
-pcap_set_fanout_linux(pcap_t *p, uint16_t mode, uint16_t group_id)
+pcap_set_fanout_linux(pcap_t *p, int enable, uint16_t mode, uint16_t group_id)
 {
 #ifdef PACKET_FANOUT
 	if (pcap_check_activated(p)) {
 		return (PCAP_ERROR_ACTIVATED);
 	}
 
-	if (mode >= 0) {
-		p->opt.fanout = (((int)mode) << 16) | ((int)group_id & 0xffff);
-	} else {
-		p->opt.fanout = -1;
-	}
+	p->opt.fanout_enabled = 1;
+	p->opt.fanout_opt = (((int)mode) << 16) | ((int)group_id & 0xffff);
 
 	return 0;
 #else

diff --git a/pcap.c b/pcap.c
@@ -2365,7 +2365,8 @@ pcap_create_common(char *ebuf, size_t size)
 	 */
 #ifdef __linux__
 	p->opt.protocol = 0;
-	p->opt.fanout = -1;
+	p->opt.fanout_enabled = 0;
+	p->opt.fanout_opt = 0;
 #endif
 #ifdef _WIN32
 	p->opt.nocapture_local = 0;

diff --git a/pcap/pcap.h b/pcap/pcap.h
@@ -352,7 +352,7 @@ PCAP_API const char *pcap_tstamp_type_val_to_description(int);
 
 #ifdef __linux__
 PCAP_API int	pcap_set_protocol_linux(pcap_t *, int);
-PCAP_API int	pcap_set_fanout_linux(pcap_t *, uint16_t, uint16_t);
+PCAP_API int	pcap_set_fanout_linux(pcap_t *, int, uint16_t, uint16_t);
 #endif
 
 /*

diff --git a/pcap_set_fanout_linux.3pcap b/pcap_set_fanout_linux.3pcap
@@ -28,25 +28,26 @@ among processes
 #include <pcap/pcap.h>
 .LP
 .ft B
-int pcap_set_fanout_linux(pcap_t *p, int8_t mode, uint16_t group_id);
+int pcap_set_fanout_linux(pcap_t *p, int enable, uint16_t mode, uint16_t group_id);
 .ft
 .fi
 .SH DESCRIPTION
-On network intreface devices on Linux,
+On Linux network interface devices,
 .B pcap_set_fanout_linux()
 sets the fanout configuration to be used in the
 .BR socket (2)
 call to create a capture socket when the handle is activated.
 This function is only provided on Linux, and, if it is used on any device other
 than a network interface, it will have no effect.
 .LP
+.IR enable
+is a boolean flag to control if fanout is enabled (default is FALSE).
+.LP
 .IR mode
 is the fanout mode and flags to use. More information on the various modes can
 be found in
 .BR packet (7)\c
-\&. If
-.IR mode
-is lower than 0, fanout will be disabled (this is the default).
+\&.
 .LP
 .IR group_id
 is a unique identifier of the socket group.