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 <netdissect-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
setsignal(int sig,RETSIGTYPE (* func)(int))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 
91