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1 office 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 #ifdef HAVE_CONFIG_H
23 #include "config.h"
24 #endif
25  
26 #include <tcpdump-stdinc.h>
27  
28 #include <signal.h>
29 #ifdef HAVE_SIGACTION
30 #include <string.h>
31 #endif
32  
33 #ifdef HAVE_OS_PROTO_H
34 #include "os-proto.h"
35 #endif
36  
37 #include "setsignal.h"
38  
39 /*
40 * An OS-independent signal() with, whenever possible, partial BSD
41 * semantics, i.e. the signal handler is restored following service
42 * of the signal, but system calls are *not* restarted, so that if
43 * "pcap_breakloop()" is called in a signal handler in a live capture,
44 * the read/recvfrom/whatever in the live capture doesn't get restarted,
45 * it returns -1 and sets "errno" to EINTR, so we can break out of the
46 * live capture loop.
47 *
48 * We use "sigaction()" if available. We don't specify that the signal
49 * should restart system calls, so that should always do what we want.
50 *
51 * Otherwise, if "sigset()" is available, it probably has BSD semantics
52 * while "signal()" has traditional semantics, so we use "sigset()"; it
53 * might cause system calls to be restarted for the signal, however.
54 * I don't know whether, in any systems where it did cause system calls to
55 * be restarted, there was a way to ask it not to do so; there may no
56 * longer be any interesting systems without "sigaction()", however,
57 * and, if there are, they might have "sigvec()" with SV_INTERRUPT
58 * (which I think first appeared in 4.3BSD).
59 *
60 * Otherwise, we use "signal()" - which means we might get traditional
61 * semantics, wherein system calls don't get restarted *but* the
62 * signal handler is reset to SIG_DFL and the signal is not blocked,
63 * so that a subsequent signal would kill the process immediately.
64 *
65 * Did I mention that signals suck? At least in POSIX-compliant systems
66 * they suck far less, as those systems have "sigaction()".
67 */
68 RETSIGTYPE
69 (*setsignal (int sig, RETSIGTYPE (*func)(int)))(int)
70 {
71 #ifdef HAVE_SIGACTION
72 struct sigaction old, new;
73  
74 memset(&new, 0, sizeof(new));
75 new.sa_handler = func;
76 if (sig == SIGCHLD)
77 new.sa_flags = SA_RESTART;
78 if (sigaction(sig, &new, &old) < 0)
79 return (SIG_ERR);
80 return (old.sa_handler);
81  
82 #else
83 #ifdef HAVE_SIGSET
84 return (sigset(sig, func));
85 #else
86 return (signal(sig, func));
87 #endif
88 #endif
89 }
90