Add APIs to put a "pcap_t" into or out of non-blocking mode, and to get

the current state of non-blocking mode; this allows us to implement, for
example, memory-mapped capture devices, where "pcap_read()" uses
"select()" or "poll()" to wait for packets to arrive, and hide that
implementation detail from applications using this API
("pcap_setnonblock()" would set or clear a non-blocking mode flag in the
"pcap_t", and the "select()" or "poll()" would not be done if the
"pcap_t" is in non-blocking mode).

pcap.3

@@ -1,4 +1,4 @@
-.\" @(#) $Header: /tcpdump/master/libpcap/Attic/pcap.3,v 1.27 2001-10-28 03:54:57 guy Exp $
+.\" @(#) $Header: /tcpdump/master/libpcap/Attic/pcap.3,v 1.28 2001-12-09 05:10:02 guy Exp $
 .\"
 .\" Copyright (c) 1994, 1996, 1997
 .\"	The Regents of the University of California.  All rights reserved.
@@ -76,6 +76,11 @@ u_char *pcap_next(pcap_t *p, struct pcap_pkthdr *h)
 .ft
 .LP
 .ft B
+int pcap_setnonblock(pcap_t *, int nonblock, char *errbuf);
+int pcap_getnonblock(pcap_t *p, char *errbuf);
+.ft
+.LP
+.ft B
 int pcap_datalink(pcap_t *p)
 int pcap_snapshot(pcap_t *p)
 int pcap_is_swapped(pcap_t *p)
@@ -481,6 +486,34 @@ when that BPF program is no longer needed, for example after it
 has been made the filter program for a pcap structure by a call to
 .BR pcap_setfilter() .
 .PP
+.B pcap_setnonblock()
+puts a capture descriptor, opened with
+.BR pcap_open_live() ,
+into ``non-blocking'' mode, or takes it out of ``non-blocking'' mode,
+depending on whether the
+.I nonblock
+argument is non-zero or zero.  It has no effect on ``savefiles''.
+If there is an error, \-1 is returned and
+.I errbuf
+is filled in with an appropriate error message.
+In
+``non-blocking'' mode, an attempt to read from the capture descriptor
+with
+.B pcap_dispatch()
+will, if no packets are currently available to be read, return 0
+immediately rather than blocking waiting for packets to arrive.
+.B pcap_loop()
+and
+.B pcap_next()
+will not work in ``non-blocking'' mode.
+.PP
+.B pcap_getnonblock()
+returns the current ``non-blocking'' state of the capture descriptor; it
+always returns 0 on ``savefiles''.
+If there is an error, \-1 is returned and
+.I errbuf
+is filled in with an appropriate error message.
+.PP
 .B pcap_datalink()
 returns the link layer type; link layer types it can return include:
 .PP

pcap.c

@@ -33,7 +33,7 @@
 
 #ifndef lint
 static const char rcsid[] =
-    "@(#) $Header: /tcpdump/master/libpcap/pcap.c,v 1.36 2000-12-16 10:43:31 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/pcap.c,v 1.37 2001-12-09 05:10:03 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -46,6 +46,8 @@ static const char rcsid[] =
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
 
 #ifdef HAVE_OS_PROTO_H
 #include "os-proto.h"
@@ -168,6 +170,65 @@ pcap_geterr(pcap_t *p)
 	return (p->errbuf);
 }
 
+/*
+ * NOTE: in the future, these may need to call platform-dependent routines,
+ * e.g. on platforms with memory-mapped packet-capture mechanisms where
+ * "pcap_read()" uses "select()" or "poll()" to wait for packets to arrive.
+ */
+int
+pcap_getnonblock(pcap_t *p, char *errbuf)
+{
+	int fdflags;
+
+	if (p->sf.rfile != NULL) {
+		/*
+		 * This is a savefile, not a live capture file, so
+		 * never say it's in non-blocking mode.
+		 */
+		return (0);
+	}
+	fdflags = fcntl(p->fd, F_GETFL, 0);
+	if (fdflags == -1) {
+		snprintf(p->errbuf, PCAP_ERRBUF_SIZE, "F_GETFL: %s",
+		    pcap_strerror(errno));
+		return (-1);
+	}
+	if (fdflags & O_NONBLOCK)
+		return (1);
+	else
+		return (0);
+}
+
+int
+pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf)
+{
+	int fdflags;
+
+	if (p->sf.rfile != NULL) {
+		/*
+		 * This is a savefile, not a live capture file, so
+		 * ignore requests to put it in non-blocking mode.
+		 */
+		return (0);
+	}
+	fdflags = fcntl(p->fd, F_GETFL, 0);
+	if (fdflags == -1) {
+		snprintf(p->errbuf, PCAP_ERRBUF_SIZE, "F_GETFL: %s",
+		    pcap_strerror(errno));
+		return (-1);
+	}
+	if (nonblock)
+		fdflags |= O_NONBLOCK;
+	else
+		fdflags &= ~O_NONBLOCK;
+	if (fcntl(p->fd, F_SETFL, fdflags) == -1) {
+		snprintf(p->errbuf, PCAP_ERRBUF_SIZE, "F_SETFL: %s",
+		    pcap_strerror(errno));
+		return (-1);
+	}
+	return (fdflags);
+}
+
 /*
  * Not all systems have strerror().
  */

pcap.h

@@ -31,7 +31,7 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- * @(#) $Header: /tcpdump/master/libpcap/pcap.h,v 1.33 2001-10-28 02:31:50 guy Exp $ (LBL)
+ * @(#) $Header: /tcpdump/master/libpcap/pcap.h,v 1.34 2001-12-09 05:10:03 guy Exp $ (LBL)
  */
 
 #ifndef lib_pcap_h
@@ -170,6 +170,8 @@ const u_char*
 	pcap_next(pcap_t *, struct pcap_pkthdr *);
 int	pcap_stats(pcap_t *, struct pcap_stat *);
 int	pcap_setfilter(pcap_t *, struct bpf_program *);
+int	pcap_getnonblock(pcap_t *, char *);
+int	pcap_setnonblock(pcap_t *, int, char *);
 void	pcap_perror(pcap_t *, char *);
 char	*pcap_strerror(int);
 char	*pcap_geterr(pcap_t *);