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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
     23 static 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  */
     73 RETSIGTYPE
     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 
     94