contrib/tcpdump/setsignal.c

   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