Add a "pcap_get_selectable_fd()" API to get an FD on which you can do a

"select()" or "poll()" - or -1 if that won't work.

pcap-bpf.c

@@ -20,7 +20,7 @@
  */
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/pcap-bpf.c,v 1.69 2003-11-20 02:02:38 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/pcap-bpf.c,v 1.70 2003-11-21 10:19:33 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -33,6 +33,7 @@ static const char rcsid[] _U_ =
 #include <sys/socket.h>
 #include <sys/file.h>
 #include <sys/ioctl.h>
+#include <sys/utsname.h>
 
 #include <net/if.h>
 
@@ -495,6 +496,7 @@ pcap_open_live(const char *device, int snaplen, int promisc, int to_ms,
 #endif
 	u_int v;
 	pcap_t *p;
+	struct utsname osinfo;
 
 #ifdef HAVE_DAG_API
 	if (strstr(device, "dag")) {
@@ -760,6 +762,60 @@ pcap_open_live(const char *device, int snaplen, int promisc, int to_ms,
 	memset(p->buffer, 0x0, p->bufsize);
 #endif
 
+	/*
+	 * On most BPF platforms, either you can do a "select()" or
+	 * "poll()" on a BPF file descriptor and it works correctly,
+	 * or you can do it and it will return "readable" if the
+	 * hold buffer is full but not if the timeout expires *and*
+	 * a non-blocking read will, if the hold buffer is empty
+	 * but the store buffer isn't empty, rotate the buffers
+	 * and return what packets are available.
+	 *
+	 * In the latter case, the fact that a non-blocking read
+	 * will give you the available packets means you can work
+	 * around the failure of "select()" and "poll()" to wake up
+	 * and return "readable" when the timeout expires by using
+	 * the timeout as the "select()" or "poll()" timeout, putting
+	 * the BPF descriptor into non-blocking mode, and read from
+	 * it regardless of whether "select()" reports it as readable
+	 * or not.
+	 *
+	 * However, in FreeBSD 4.3 and 4.4, "select()" and "poll()"
+	 * won't wake up and return "readable" if the timer expires
+	 * and non-blocking reads return EWOULDBLOCK if the hold
+	 * buffer is empty, even if the store buffer is non-empty.
+	 *
+	 * This means the workaround in question won't work.
+	 *
+	 * Therefore, on FreeBSD 4.3 and 4.4, we set "p->selectable_fd"
+	 * to -1, which means "sorry, you can't use 'select()' or 'poll()'
+	 * here".  On all other BPF platforms, we set it to the FD for
+	 * the BPF device; in NetBSD, OpenBSD, and Darwin, a non-blocking
+	 * read will, if the hold buffer is empty and the store buffer
+	 * isn't empty, rotate the buffers and return what packets are
+	 * there (and in sufficiently recent versions of OpenBSD
+	 * "select()" and "poll()" should work correctly).
+	 *
+	 * XXX - what about AIX?
+	 */
+	if (uname(&osinfo) == 0) {
+		/*
+		 * We can check what OS this is.
+		 */
+		if (strcmp(osinfo.sysname, "FreeBSD") == 0 &&
+		    (strcmp(osinfo.release, "4.3") == 0 ||
+		     strcmp(osinfo.release, "4.4") == 0))
+			p->selectable_fd = -1;
+		else
+			p->selectable_fd = p->fd;
+	} else {
+		/*
+		 * We can't find out what OS this is, so assume we can
+		 * do a "select()" or "poll()".
+		 */
+		p->selectable_fd = p->fd;
+	}
+
 	p->read_op = pcap_read_bpf;
 	p->setfilter_op = pcap_setfilter_bpf;
 	p->set_datalink_op = pcap_set_datalink_bpf;

pcap-dag.c

@@ -29,7 +29,7 @@
 
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/pcap-dag.c,v 1.13 2003-11-20 02:02:38 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/pcap-dag.c,v 1.14 2003-11-21 10:19:33 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -469,6 +469,11 @@ pcap_t *dag_open_live(const char *device, int snaplen, int promisc, int to_ms, c
 	goto fail;
   }
 
+  /*
+   * "select()" and "poll()" don't (yet) work on DAG device descriptors.
+   */
+  handle->selectable_fd = -1;
+
 #ifdef linux
   handle->md.device = (char *)device;
 #else

pcap-dlpi.c

@@ -38,7 +38,7 @@
 
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/pcap-dlpi.c,v 1.93 2003-11-20 02:02:38 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/pcap-dlpi.c,v 1.94 2003-11-21 10:19:34 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -704,6 +704,12 @@ pcap_open_live(const char *device, int snaplen, int promisc, int to_ms,
 		goto bad;
 	}
 
+	/*
+	 * "p->fd" is an FD for a STREAMS device, so "select()" and
+	 * "poll()" should work on it.
+	 */
+	p->selectable_fd = p->fd;
+
 	p->read_op = pcap_read_dlpi;
 	p->setfilter_op = install_bpf_program;	/* no kernel filtering */
 	p->set_datalink_op = NULL;	/* can't change data link type */

pcap-int.h

@@ -30,7 +30,7 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- * @(#) $Header: /tcpdump/master/libpcap/pcap-int.h,v 1.57 2003-11-20 02:02:39 guy Exp $ (LBL)
+ * @(#) $Header: /tcpdump/master/libpcap/pcap-int.h,v 1.58 2003-11-21 10:19:34 guy Exp $ (LBL)
  */
 
 #ifndef pcap_int_h
@@ -101,6 +101,7 @@ struct pcap {
 	int nonblock;
 #else
 	int fd;
+	int selectable_fd;
 #endif /* WIN32 */
 	int snapshot;
 	int linktype;

pcap-linux.c

@@ -27,7 +27,7 @@
 
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/pcap-linux.c,v 1.101 2003-11-20 02:02:39 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/pcap-linux.c,v 1.102 2003-11-21 10:19:34 guy Exp $ (LBL)";
 #endif
 
 /*
@@ -397,6 +397,12 @@ pcap_open_live(const char *device, int snaplen, int promisc, int to_ms,
 		return NULL;
 	}
 
+	/*
+	 * "handle->fd" is a socket, so "select()" and "poll()"
+	 * should work on it.
+	 */
+	handle->selectable_fd = handle->fd;
+
 	handle->read_op = pcap_read_linux;
 	handle->setfilter_op = pcap_setfilter_linux;
 	handle->set_datalink_op = NULL;	/* can't change data link type */

pcap-nit.c

@@ -20,7 +20,7 @@
  */
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/pcap-nit.c,v 1.52 2003-11-20 02:02:40 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/pcap-nit.c,v 1.53 2003-11-21 10:19:35 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -280,6 +280,11 @@ pcap_open_live(const char *device, int snaplen, int promisc, int to_ms,
 		goto bad;
 	}
 
+	/*
+	 * "handle->fd" is a socket, so "select()" should work on it.
+	 */
+	p->selectable_fd = p->fd;
+
 	p->read_op = pcap_read_nit;
 	p->setfilter_op = install_bpf_program;	/* no kernel filtering */
 	p->set_datalink_op = NULL;	/* can't change data link type */

pcap-pf.c

@@ -24,7 +24,7 @@
 
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/pcap-pf.c,v 1.81 2003-11-20 02:02:40 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/pcap-pf.c,v 1.82 2003-11-21 10:19:35 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -434,6 +434,11 @@ your system may not be properly configured; see the packetfilter(4) man page\n",
 		goto bad;
 	}
 
+	/*
+	 * "select()" and "poll()" work on packetfilter devices.
+	 */
+	p->selectable_fd = p->fd;
+
 	p->read_op = pcap_read_pf;
 	p->setfilter_op = pcap_setfilter_pf;
 	p->set_datalink_op = NULL;	/* can't change data link type */

pcap-snit.c

@@ -25,7 +25,7 @@
 
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/pcap-snit.c,v 1.68 2003-11-20 02:02:40 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/pcap-snit.c,v 1.69 2003-11-21 10:19:35 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -338,6 +338,12 @@ pcap_open_live(const char *device, int snaplen, int promisc, int to_ms,
 		goto bad;
 	}
 
+	/*
+	 * "p->fd" is an FD for a STREAMS device, so "select()" and
+	 * "poll()" should work on it.
+	 */
+	p->selectable_fd = p->fd;
+
 	p->read_op = pcap_read_snit;
 	p->setfilter_op = install_bpf_program;	/* no kernel filtering */
 	p->set_datalink_op = NULL;	/* can't change data link type */

pcap-snoop.c

@@ -20,7 +20,7 @@
  */
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/pcap-snoop.c,v 1.48 2003-11-20 02:02:40 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/pcap-snoop.c,v 1.49 2003-11-21 10:19:35 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -323,6 +323,11 @@ pcap_open_live(const char *device, int snaplen, int promisc, int to_ms,
 		goto bad;
 	}
 
+	/*
+	 * "handle->fd" is a socket, so "select()" should work on it.
+	 */
+	p->selectable_fd = p->fd;
+
 	p->read_op = pcap_read_snoop;
 	p->setfilter_op = install_bpf_program;	/* no kernel filtering */
 	p->set_datalink_op = NULL;	/* can't change data link type */

pcap.3

@@ -1,4 +1,4 @@
-.\" @(#) $Header: /tcpdump/master/libpcap/Attic/pcap.3,v 1.54 2003-11-18 22:14:24 guy Exp $
+.\" @(#) $Header: /tcpdump/master/libpcap/Attic/pcap.3,v 1.55 2003-11-21 10:19:36 guy Exp $
 .\"
 .\" Copyright (c) 1994, 1996, 1997
 .\"	The Regents of the University of California.  All rights reserved.
@@ -19,7 +19,7 @@
 .\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 .\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 .\"
-.TH PCAP 3 "18 November 2003"
+.TH PCAP 3 "21 November 2003"
 .SH NAME
 pcap \- Packet Capture library
 .SH SYNOPSIS

pcap.c

@@ -33,7 +33,7 @@
 
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/pcap.c,v 1.68 2003-11-20 02:02:41 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/pcap.c,v 1.69 2003-11-21 10:19:36 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -500,6 +500,14 @@ pcap_fileno(pcap_t *p)
 #endif
 }
 
+#ifndef WIN32
+int
+pcap_get_selectable_fd(pcap_t *p)
+{
+	return (p->selectable_fd);
+}
+#endif
+
 void
 pcap_perror(pcap_t *p, char *prefix)
 {

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 1.47 2003-11-18 22:14:25 guy Exp $ (LBL)
+ * @(#) $Header: /tcpdump/master/libpcap/pcap.h,v 1.48 2003-11-21 10:19:36 guy Exp $ (LBL)
  */
 
 #ifndef lib_pcap_h
@@ -241,6 +241,13 @@ int pcap_setmintocopy(pcap_t *p, int size);
 #define MODE_CAPT 0
 #define MODE_STAT 1
 
+#else
+/*
+ * UN*X definitions
+ */
+
+int	pcap_get_selectable_fd(pcap_t *);
+
 #endif /* WIN32 */
 
 #ifdef __cplusplus

savefile.c

@@ -30,7 +30,7 @@
 
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/libpcap/savefile.c,v 1.97 2003-11-20 02:02:41 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/savefile.c,v 1.98 2003-11-21 10:19:37 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -600,6 +600,12 @@ pcap_open_offline(const char *fname, char *errbuf)
 		break;
 	}
 
+	/*
+	 * You can do "select()" and "poll()" on plain files on most
+	 * platforms, and should be able to do so on pipes.
+	 */
+	p->selectable_fd = fileno(fp);
+
 	p->read_op = pcap_offline_read;
 	p->setfilter_op = install_bpf_program;
 	p->set_datalink_op = NULL;	/* we don't support munging link-layer headers */