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116 lines
4.0 KiB
116 lines
4.0 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_BREAKLOOP 3PCAP "25 July 2018"
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.SH NAME
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pcap_breakloop \- force a pcap_dispatch() or pcap_loop() call to return
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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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void pcap_breakloop(pcap_t *);
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.ft
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.fi
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.SH DESCRIPTION
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.BR pcap_breakloop ()
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sets a flag that will force
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.BR pcap_dispatch (3PCAP)
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or
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.BR pcap_loop (3PCAP)
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to return rather than looping; they will return the number of packets
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that have been processed so far, or
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.B PCAP_ERROR_BREAK
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if no packets have been processed so far.
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.PP
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This routine is safe to use inside a signal handler on UNIX or a console
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control handler on Windows, as it merely sets a flag that is checked
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within the loop.
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.PP
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The flag is checked in loops reading packets from the OS - a signal by
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itself will not necessarily terminate those loops - as well as in loops
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processing a set of packets returned by the OS.
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.ft B
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Note that if you are catching signals on UNIX systems that support
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restarting system calls after a signal, and calling pcap_breakloop()
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in the signal handler, you must specify, when catching those signals,
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that system calls should NOT be restarted by that signal. Otherwise,
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if the signal interrupted a call reading packets in a live capture,
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when your signal handler returns after calling pcap_breakloop(), the
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call will be restarted, and the loop will not terminate until more
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packets arrive and the call completes.
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.ft R
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.PP
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.ft B
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Note also that, in a multi-threaded application, if one thread is
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blocked in pcap_dispatch(), pcap_loop(), pcap_next(3PCAP), or pcap_next_ex(3PCAP),
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a call to pcap_breakloop() in a different thread will not unblock that
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thread.
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.ft R
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You will need to use whatever mechanism the OS provides for
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breaking a thread out of blocking calls in order to unblock the thread,
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such as thread cancellation or thread signalling in systems that support
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POSIX threads, or
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.BR SetEvent ()
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on the result of
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.BR pcap_getevent ()
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on a
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.B pcap_t
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on which the thread is blocked on Windows. Asynchronous procedure calls
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will not work on Windows, as a thread blocked on a
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.B pcap_t
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will not be in an alertable state.
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.ft R
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.PP
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Note that
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.BR pcap_next ()
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and
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.BR pcap_next_ex ()
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will, on some platforms, loop reading packets from the OS; that loop
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will not necessarily be terminated by a signal, so
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.BR pcap_breakloop ()
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should be used to terminate packet processing even if
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.BR pcap_next ()
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or
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.BR pcap_next_ex ()
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is being used.
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.PP
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.BR pcap_breakloop ()
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does not guarantee that no further packets will be processed by
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.BR pcap_dispatch ()
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or
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.BR pcap_loop ()
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after it is called; at most one more packet might be processed.
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.PP
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If
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.B PCAP_ERROR_BREAK
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is returned from
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.BR pcap_dispatch ()
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or
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.BR pcap_loop (),
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the flag is cleared, so a subsequent call will resume reading packets.
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If a positive number is returned, the flag is not cleared, so a
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subsequent call will return
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.B PCAP_ERROR_BREAK
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and clear the flag.
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.SH SEE ALSO
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.BR pcap (3PCAP)
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