Remove the "select()" from the code path for reading live captures on

Linux; Linux isn't the only platform whose kernel doesn't support a
read timeout, and even some that *do* don't start the timer until at
least one packet has arrived (Solaris, for example), so no portable
application can depend on "pcap_dispatch()", say, blocking for no longer
than the timeout - they must do a "select()" themselves.  For
applications that do the "select()" themselves, or that don't need the
timeout for polling (tcpdump, for example), doing a "select()" in
libpcap just adds another system call to the code path.

diff --git a/pcap-linux.c b/pcap-linux.c
index f2f336df8f92d0bcb8e33c408bfadca3e78b846b..b5be6ce2fd90f7ff281800bbd4e590e0184965c2 100644 (file)
--- a/pcap-linux.c
+++ b/pcap-linux.c
@@ -26,7 +26,7 @@
  */
 #ifndef lint
 static const char rcsid[] =
-    "@(#) $Header: /tcpdump/master/libpcap/pcap-linux.c,v 1.50 2000-12-23 07:50:18 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/pcap-linux.c,v 1.51 2001-01-03 01:06:16 guy Exp $ (LBL)";
 #endif
 
 /*
@@ -194,27 +194,6 @@ pcap_open_live(char *device, int snaplen, int promisc, int to_ms, char *ebuf)
                return NULL;
        }
 
-       /* 
-        * Okay, now we have a packet stream open. Maybe we need to handle 
-        * a timeout? In that case we set the filehandle to nonblocking 
-        * so pcap_read can try reading the fd and call select if no data
-        * is available at first. 
-        */
-
-       if (to_ms > 0) {
-               int     flags = fcntl(handle->fd, F_GETFL);
-               if (flags != -1) {
-                       flags |= O_NONBLOCK;
-                       flags = fcntl(handle->fd, F_SETFL, flags);
-               }
-               if (flags == -1) {
-                       snprintf(ebuf, PCAP_ERRBUF_SIZE, "fcntl: %s",
-                                pcap_strerror(errno));
-                       pcap_close(handle);
-                       return NULL;
-               }
-       }
-
        return handle;
 }
 
@@ -222,70 +201,15 @@ pcap_open_live(char *device, int snaplen, int promisc, int to_ms, char *ebuf)
  *  Read at most max_packets from the capture stream and call the callback
  *  for each of them. Returns the number of packets handled or -1 if an
  *  error occured. 
- *  
- *  XXX: Can I rely on the Linux-specified behaviour of select (returning
- *  the time left in the timeval structure)? I really don't want to query
- *  the system time before each select call...
- *  
- *  pcap_read currently gets not only a packet from the kernel but also
- *  the sockaddr_ll returned as source of the packet. This way we can at
- *  some time extend tcpdump and libpcap to sniff on all devices at a time
- *  and find the right printing routine by using the information in the
- *  sockaddr_ll structure.
  */
 int
 pcap_read(pcap_t *handle, int max_packets, pcap_handler callback, u_char *user)
 {
-       int             status, packets;
-       fd_set          read_fds;
-       struct timeval  tv;
-
-       /*
-        * Fill in a timeval structure for select if we need to obeye a
-        * timeout.
-        */
-       if (handle->md.timeout > 0) {
-               tv.tv_usec      = (handle->md.timeout % 1000) * 1000;
-               tv.tv_sec       = (handle->md.timeout / 1000);
-       }
-
        /*
-        * Read packets until the packet limit has been reached or 
-        * an error occured while reading. Call the user function 
-        * for each received packet.
+        * Currently, on Linux only one packet is delivered per read,
+        * so we don't loop.
         */
-       for (packets = 0; max_packets == -1 || packets < max_packets;)
-       {
-               status = pcap_read_packet(handle, callback, user);
-
-               if (status > 0) {
-                       packets += status;
-                       continue;
-               } else if (status == -1)
-                       return -1;
-
-               /* 
-                * If no packet is available we go to sleep. FIXME: This
-                * might be better implemented using poll(?)
-                */
-               FD_ZERO(&read_fds);
-               FD_SET(handle->fd, &read_fds);
-               status = select(handle->fd + 1, 
-                               &read_fds, NULL, NULL, &tv);
-
-               if (status == -1) {
-                       if (errno == EINTR)
-                               return packets;
-                       snprintf(handle->errbuf, sizeof(handle->errbuf),
-                                "select: %s", pcap_strerror(errno));
-                       return -1;
-               } 
-               else if (status == 0 || 
-                          (tv.tv_usec == 0 && tv.tv_sec == 0))
-                       return packets;
-       }
-
-       return packets;
+       return pcap_read_packet(handle, callback, user);
 }
 
 /*