PCAP_GET_SELECTABLE_FD(3)				     Library Functions Manual					 PCAP_GET_SELECTABLE_FD(3)

NAME

       pcap_get_selectable_fd - get a file descriptor on which a select() can be done for a live capture

SYNOPSIS

       #include <pcap/pcap.h>

       int pcap_get_selectable_fd(pcap_t *p);

DESCRIPTION

       pcap_get_selectable_fd()  returns, on UNIX, a file descriptor number for a file descriptor on which one can do a select() or poll() to wait
       for it to be possible to read packets without blocking, if such a descriptor exists, or -1, if no such  descriptor  exists.   Some  network
       devices	opened	with  pcap_create() and pcap_activate(), or with pcap_open_live(), do not support select() or poll() (for example, regular
       network devices on FreeBSD 4.3 and 4.4, and Endace DAG devices), so -1 is returned for those devices.

       Note  that  on  most  versions  of  most  BSDs  (including  Mac	OS  X)	select()  and  poll()  do  not	work  correctly  on  BPF  devices;
       pcap_get_selectable_fd()  will  return  a  file	descriptor  on most of those versions (the exceptions being FreeBSD 4.3 and 4.4), a simple
       select() or poll() will not return even after the read timeout expires.	To work around this, an application that uses select()	or  poll()
       to  wait  for  packets to arrive must put the pcap_t in non-blocking mode, and must arrange that the select() or poll() have a timeout less
       than or equal to the read timeout, and must try to read packets after that timeout expires, regardless of whether select() or poll()  indi-
       cated  that  the  file descriptor for the pcap_t is ready to be read or not.  (That workaround will not work in FreeBSD 4.3 and later; how-
       ever, in FreeBSD 4.6 and later, select() and poll() work correctly on BPF devices, so the workaround isn't necessary, although it  does	no
       harm.)

       Note  also that poll() doesn't work on character special files, including BPF devices, in Mac OS X 10.4 and 10.5, so, while select() can be
       used on the descriptor returned by pcap_get_selectable_fd(), poll() cannot be used on it those versions of Mac OS X.   Kqueues  also  don't
       work  on  that descriptor.  poll(), but not kqueues, work on that descriptor in Mac OS X releases prior to 10.4; poll() and kqueues work on
       that descriptor in Mac OS X 10.6 and later.

       pcap_get_selectable_fd() is not available on Windows.

RETURN VALUE

       A selectable file descriptor is returned if one exists; otherwise, -1 is returned.

SEE ALSO

       pcap(3), select(2), poll(2)

								   5 April 2008 					 PCAP_GET_SELECTABLE_FD(3)