Manual Reference Pages - PCAP_GET_SELECTABLE_FD (3)
pcap_get_selectable_fd - get a file descriptor on which a select() can
be done for a live capture
int pcap_get_selectable_fd(pcap_t *p);
pcap_get_selectable_fd() returns, on UNIX, a file descriptor number for a file descriptor on
which one can
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_activate(), or with
pcap_open_live(), do not support
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 in:
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), but a simple
poll() will not indicate that the descriptor is readable until a full buffers
worth of packets is received, even if the read timeout expires before
then. To work around this, an application that uses
poll() to wait for packets to arrive must put the
pcap_t in non-blocking mode, and must arrange that the
poll() have a timeout less than or equal to the read timeout,
and must try to read packets after that timeout expires, regardless of
poll() indicated 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; however, in FreeBSD 4.6 and later,
poll() work correctly on BPF devices, so the workaround isnt necessary,
although it does no harm.)
FreeBSD prior to FreeBSD 4.6;
NetBSD prior to NetBSD 3.0;
OpenBSD prior to OpenBSD 2.4;
Mac OS X prior to Mac OS X 10.7;
Note also that
poll() doesnt 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
poll() cannot be used on it those versions of Mac OS X. Kqueues also dont
work on that descriptor.
poll(), but not kqueues, work on that descriptor in Mac OS X releases prior to
poll() and kqueues work on that descriptor in Mac OS X 10.6 and later.
pcap_get_selectable_fd() is not available on Windows.
A selectable file descriptor is returned if one exists; otherwise, -1
pcap(3), select(2), poll(2)
|--> ||PCAP_GET_SELECTABLE_FD (3) ||5 April 2008 |
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