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133 lines
4.1 KiB
133 lines
4.1 KiB
.\" Copyright (c) 1994, 1996, 1997 |
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.\" The Regents of the University of California. All rights reserved. |
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.\" |
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.\" Redistribution and use in source and binary forms, with or without |
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.\" modification, are permitted provided that: (1) source code distributions |
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.\" retain the above copyright notice and this paragraph in its entirety, (2) |
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.\" distributions including binary code include the above copyright notice and |
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.\" this paragraph in its entirety in the documentation or other materials |
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.\" provided with the distribution, and (3) all advertising materials mentioning |
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.\" features or use of this software display the following acknowledgement: |
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.\" ``This product includes software developed by the University of California, |
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.\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of |
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.\" the University nor the names of its contributors may be used to endorse |
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.\" or promote products derived from this software without specific prior |
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.\" written permission. |
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.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED |
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.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF |
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. |
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.\" |
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.TH PCAP_GET_SELECTABLE_FD 3PCAP "18 October 2014" |
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.SH NAME |
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pcap_get_selectable_fd \- get a file descriptor on which a select() can |
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be done for a live capture |
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.SH SYNOPSIS |
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.nf |
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.ft B |
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#include <pcap/pcap.h> |
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.ft |
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.LP |
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.ft B |
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int pcap_get_selectable_fd(pcap_t *p); |
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.ft |
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.fi |
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.SH DESCRIPTION |
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.B pcap_get_selectable_fd() |
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returns, on UNIX, a file descriptor number for a file descriptor on |
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which one can |
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do a |
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.BR select() , |
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.BR poll() , |
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or other such call |
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to wait for it to be possible to read packets without blocking, if such |
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a descriptor exists, or \-1, if no such descriptor exists. Some network |
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devices opened with |
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.B pcap_create() |
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and |
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.BR pcap_activate() , |
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or with |
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.BR pcap_open_live() , |
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do not support |
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.B select() |
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or |
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.B poll() |
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(for example, regular network devices on FreeBSD 4.3 and 4.4, and Endace |
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DAG devices), so \-1 is returned for those devices. |
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.PP |
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Note that a descriptor on which a read can be done without blocking may, |
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on some platforms, not have any packets to read if the read timeout has |
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expired. A call to |
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.B pcap_dispatch() |
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will return 0 in this case, but will not block. |
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.PP |
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Note that in: |
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.IP |
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FreeBSD prior to FreeBSD 4.6; |
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.IP |
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NetBSD prior to NetBSD 3.0; |
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.IP |
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OpenBSD prior to OpenBSD 2.4; |
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.IP |
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Mac OS X prior to Mac OS X 10.7; |
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.PP |
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.B select() |
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and |
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.B poll() |
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do not work correctly on BPF devices; |
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.B pcap_get_selectable_fd() |
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will return a file descriptor on most of those versions (the exceptions |
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being FreeBSD 4.3 and 4.4), but a simple |
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.B select() |
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or |
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.B poll() |
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will not indicate that the descriptor is readable until a full buffer's |
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worth of packets is received, even if the read timeout expires before |
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then. To work around this, an application that uses |
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.B select() |
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or |
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.B poll() |
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to wait for packets to arrive must put the |
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.B pcap_t |
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in non-blocking mode, and must arrange that the |
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.B select() |
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or |
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.B poll() |
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have a timeout less than or equal to the read timeout, |
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and must try to read packets after that timeout expires, regardless of |
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whether |
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.B select() |
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or |
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.B poll() |
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indicated that the file descriptor for the |
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.B pcap_t |
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is ready to be read or not. (That workaround will not work in FreeBSD |
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4.3 and later; however, in FreeBSD 4.6 and later, |
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.B select() |
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and |
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.B poll() |
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work correctly on BPF devices, so the workaround isn't necessary, |
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although it does no harm.) |
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.PP |
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Note also that |
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.B poll() |
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doesn't work on character special files, including BPF devices, in Mac |
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OS X 10.4 and 10.5, so, while |
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.B select() |
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can be used on the descriptor returned by |
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.BR pcap_get_selectable_fd() , |
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.B poll() |
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cannot be used on it those versions of Mac OS X. Kqueues also don't |
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work on that descriptor. |
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.BR poll() , |
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but not kqueues, work on that descriptor in Mac OS X releases prior to |
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10.4; |
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.B poll() |
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and kqueues work on that descriptor in Mac OS X 10.6 and later. |
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.PP |
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.B pcap_get_selectable_fd() |
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is not available on Windows. |
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.SH RETURN VALUE |
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A selectable file descriptor is returned if one exists; otherwise, \-1 |
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is returned. |
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.SH SEE ALSO |
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pcap(3PCAP), select(2), poll(2)
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