/* * Copyright (c) 1997 *	The Regents of the University of California.  All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that: (1) source code distributions * retain the above copyright notice and this paragraph in its entirety, (2) * distributions including binary code include the above copyright notice and * this paragraph in its entirety in the documentation or other materials * provided with the distribution, and (3) all advertising materials mentioning * features or use of this software display the following acknowledgement: * ``This product includes software developed by the University of California, * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of * the University nor the names of its contributors may be used to endorse * or promote products derived from this software without specific prior * written permission. * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. */#ifndef lintstatic const char rcsid[] _U_ =    "@(#) $Header: /tcpdump/master/tcpdump/setsignal.c,v 1.11 2003-11-16 09:36:42 guy Exp $ (LBL)";#endif#ifdef HAVE_CONFIG_H#include "config.h"#endif#include <tcpdump-stdinc.h>#include <signal.h>#ifdef HAVE_SIGACTION#include <string.h>#endif#ifdef HAVE_OS_PROTO_H#include "os-proto.h"#endif#include "setsignal.h"/* * An OS-independent signal() with, whenever possible, partial BSD * semantics, i.e. the signal handler is restored following service * of the signal, but system calls are *not* restarted, so that if * "pcap_breakloop()" is called in a signal handler in a live capture, * the read/recvfrom/whatever in the live capture doesn't get restarted, * it returns -1 and sets "errno" to EINTR, so we can break out of the * live capture loop. * * We use "sigaction()" if available.  We don't specify that the signal * should restart system calls, so that should always do what we want. * * Otherwise, if "sigset()" is available, it probably has BSD semantics * while "signal()" has traditional semantics, so we use "sigset()"; it * might cause system calls to be restarted for the signal, however. * I don't know whether, in any systems where it did cause system calls to * be restarted, there was a way to ask it not to do so; there may no * longer be any interesting systems without "sigaction()", however, * and, if there are, they might have "sigvec()" with SV_INTERRUPT * (which I think first appeared in 4.3BSD). * * Otherwise, we use "signal()" - which means we might get traditional * semantics, wherein system calls don't get restarted *but* the * signal handler is reset to SIG_DFL and the signal is not blocked, * so that a subsequent signal would kill the process immediately. * * Did I mention that signals suck?  At least in POSIX-compliant systems * they suck far less, as those systems have "sigaction()". */RETSIGTYPE(*setsignal (int sig, RETSIGTYPE (*func)(int)))(int){#ifdef HAVE_SIGACTION	struct sigaction old, new;	memset(&new, 0, sizeof(new));	new.sa_handler = func;	if (sigaction(sig, &new, &old) < 0)		return (SIG_ERR);	return (old.sa_handler);#else#ifdef HAVE_SIGSET	return (sigset(sig, func));#else	return (signal(sig, func));#endif#endif}