Move tcpdump-3.9/ to tcpdump/. No need for a versioned dir.
[dragonfly.git] / contrib / tcpdump / setsignal.c
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c8cf0f94
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1/*
2 * Copyright (c) 1997
3 * The Regents of the University of California. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that: (1) source code distributions
7 * retain the above copyright notice and this paragraph in its entirety, (2)
8 * distributions including binary code include the above copyright notice and
9 * this paragraph in its entirety in the documentation or other materials
10 * provided with the distribution, and (3) all advertising materials mentioning
11 * features or use of this software display the following acknowledgement:
12 * ``This product includes software developed by the University of California,
13 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
14 * the University nor the names of its contributors may be used to endorse
15 * or promote products derived from this software without specific prior
16 * written permission.
17 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
18 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
19 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
20 */
21
22#ifndef lint
23static const char rcsid[] _U_ =
24 "@(#) $Header: /tcpdump/master/tcpdump/setsignal.c,v 1.11 2003/11/16 09:36:42 guy Exp $ (LBL)";
25#endif
26
27#ifdef HAVE_CONFIG_H
28#include "config.h"
29#endif
30
31#include <tcpdump-stdinc.h>
32
33#include <signal.h>
34#ifdef HAVE_SIGACTION
35#include <string.h>
36#endif
37
38#ifdef HAVE_OS_PROTO_H
39#include "os-proto.h"
40#endif
41
42#include "setsignal.h"
43
44/*
45 * An OS-independent signal() with, whenever possible, partial BSD
46 * semantics, i.e. the signal handler is restored following service
47 * of the signal, but system calls are *not* restarted, so that if
48 * "pcap_breakloop()" is called in a signal handler in a live capture,
49 * the read/recvfrom/whatever in the live capture doesn't get restarted,
50 * it returns -1 and sets "errno" to EINTR, so we can break out of the
51 * live capture loop.
52 *
53 * We use "sigaction()" if available. We don't specify that the signal
54 * should restart system calls, so that should always do what we want.
55 *
56 * Otherwise, if "sigset()" is available, it probably has BSD semantics
57 * while "signal()" has traditional semantics, so we use "sigset()"; it
58 * might cause system calls to be restarted for the signal, however.
59 * I don't know whether, in any systems where it did cause system calls to
60 * be restarted, there was a way to ask it not to do so; there may no
61 * longer be any interesting systems without "sigaction()", however,
62 * and, if there are, they might have "sigvec()" with SV_INTERRUPT
63 * (which I think first appeared in 4.3BSD).
64 *
65 * Otherwise, we use "signal()" - which means we might get traditional
66 * semantics, wherein system calls don't get restarted *but* the
67 * signal handler is reset to SIG_DFL and the signal is not blocked,
68 * so that a subsequent signal would kill the process immediately.
69 *
70 * Did I mention that signals suck? At least in POSIX-compliant systems
71 * they suck far less, as those systems have "sigaction()".
72 */
73RETSIGTYPE
74(*setsignal (int sig, RETSIGTYPE (*func)(int)))(int)
75{
76#ifdef HAVE_SIGACTION
77 struct sigaction old, new;
78
79 memset(&new, 0, sizeof(new));
80 new.sa_handler = func;
81 if (sigaction(sig, &new, &old) < 0)
82 return (SIG_ERR);
83 return (old.sa_handler);
84
85#else
86#ifdef HAVE_SIGSET
87 return (sigset(sig, func));
88#else
89 return (signal(sig, func));
90#endif
91#endif
92}
93