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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 #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 
     91