dist/tcpdump/setsignal.c

   1 /*      $NetBSD$        */
   2
   3 /*
   4  * Copyright (c) 1997
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that: (1) source code distributions
   9  * retain the above copyright notice and this paragraph in its entirety, (2)
  10  * distributions including binary code include the above copyright notice and
  11  * this paragraph in its entirety in the documentation or other materials
  12  * provided with the distribution, and (3) all advertising materials mentioning
  13  * features or use of this software display the following acknowledgement:
  14  * ``This product includes software developed by the University of California,
  15  * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
  16  * the University nor the names of its contributors may be used to endorse
  17  * or promote products derived from this software without specific prior
  18  * written permission.
  19  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
  20  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
  21  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  22  */
  23
  24 #include <sys/cdefs.h>
  25 #ifndef lint
  26 #if 0
  27 static const char rcsid[] _U_ =
  28     "@(#) Header: /tcpdump/master/tcpdump/setsignal.c,v 1.11 2003/11/16 09:36:42 guy Exp (LBL)";
  29 #else
  30 __RCSID("$NetBSD: tcpdump2rcsid.ex,v 1.1 2001/06/25 20:09:58 itojun Exp $");
  31 #endif
  32 #endif
  33
  34 #ifdef HAVE_CONFIG_H
  35 #include "config.h"
  36 #endif
  37
  38 #include <tcpdump-stdinc.h>
  39
  40 #include <signal.h>
  41 #ifdef HAVE_SIGACTION
  42 #include <string.h>
  43 #endif
  44
  45 #ifdef HAVE_OS_PROTO_H
  46 #include "os-proto.h"
  47 #endif
  48
  49 #include "setsignal.h"
  50
  51 /*
  52  * An OS-independent signal() with, whenever possible, partial BSD
  53  * semantics, i.e. the signal handler is restored following service
  54  * of the signal, but system calls are *not* restarted, so that if
  55  * "pcap_breakloop()" is called in a signal handler in a live capture,
  56  * the read/recvfrom/whatever in the live capture doesn't get restarted,
  57  * it returns -1 and sets "errno" to EINTR, so we can break out of the
  58  * live capture loop.
  59  *
  60  * We use "sigaction()" if available.  We don't specify that the signal
  61  * should restart system calls, so that should always do what we want.
  62  *
  63  * Otherwise, if "sigset()" is available, it probably has BSD semantics
  64  * while "signal()" has traditional semantics, so we use "sigset()"; it
  65  * might cause system calls to be restarted for the signal, however.
  66  * I don't know whether, in any systems where it did cause system calls to
  67  * be restarted, there was a way to ask it not to do so; there may no
  68  * longer be any interesting systems without "sigaction()", however,
  69  * and, if there are, they might have "sigvec()" with SV_INTERRUPT
  70  * (which I think first appeared in 4.3BSD).
  71  *
  72  * Otherwise, we use "signal()" - which means we might get traditional
  73  * semantics, wherein system calls don't get restarted *but* the
  74  * signal handler is reset to SIG_DFL and the signal is not blocked,
  75  * so that a subsequent signal would kill the process immediately.
  76  *
  77  * Did I mention that signals suck?  At least in POSIX-compliant systems
  78  * they suck far less, as those systems have "sigaction()".
  79  */
  80 RETSIGTYPE
  81 (*setsignal (int sig, RETSIGTYPE (*func)(int)))(int)
  82 {
  83 #ifdef HAVE_SIGACTION
  84         struct sigaction old, new;
  85
  86         memset(&new, 0, sizeof(new));
  87         new.sa_handler = func;
  88         if (sigaction(sig, &new, &old) < 0)
  89                 return (SIG_ERR);
  90         return (old.sa_handler);
  91
  92 #else
  93 #ifdef HAVE_SIGSET
  94         return (sigset(sig, func));
  95 #else
  96         return (signal(sig, func));
  97 #endif
  98 #endif
  99 }
 100