The Tcpdump Group git mirrors - tcpdump/blob - 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
  23 #ifdef HAVE_CONFIG_H
  24 #include "config.h"
  25 #endif
  26
  27 #include <tcpdump-stdinc.h>
  28
  29
  30 #include "interface.h"
  31
  32 #ifndef lint
  33 static const char rcsid[] _U_ =
  34     "@(#) $Header: /tcpdump/master/tcpdump/setsignal.c,v 1.9.2.1 2003-11-15 22:29:17 guy Exp $ (LBL)";
  35 #endif
  36
  37 #include <signal.h>
  38 #ifdef HAVE_SIGACTION
  39 #include <string.h>
  40 #endif
  41
  42 #ifdef HAVE_OS_PROTO_H
  43 #include "os-proto.h"
  44 #endif
  45
  46 #include "setsignal.h"
  47
  48 /*
  49  * An OS-independent signal() with, whenever possible, partial BSD
  50  * semantics, i.e. the signal handler is restored following service
  51  * of the signal, but system calls are *not* restarted, so that if
  52  * "pcap_breakloop()" is called in a signal handler in a live capture,
  53  * the read/recvfrom/whatever in the live capture doesn't get restarted,
  54  * it returns -1 and sets "errno" to EINTR, so we can break out of the
  55  * live capture loop.
  56  *
  57  * We use "sigaction()" if available.  We don't specify that the signal
  58  * should restart system calls, so that should always do what we want.
  59  *
  60  * Otherwise, if "sigset()" is available, it probably has BSD semantics
  61  * while "signal()" has traditional semantics, so we use "sigset()"; it
  62  * might cause system calls to be restarted for the signal, however.
  63  * I don't know whether, in any systems where it did cause system calls to
  64  * be restarted, there was a way to ask it not to do so; there may no
  65  * longer be any interesting systems without "sigaction()", however,
  66  * and, if there are, they might have "sigvec()" with SV_INTERRUPT
  67  * (which I think first appeared in 4.3BSD).
  68  *
  69  * Otherwise, we use "signal()" - which means we might get traditional
  70  * semantics, wherein system calls don't get restarted *but* the
  71  * signal handler is reset to SIG_DFL and the signal is not blocked,
  72  * so that a subsequent signal would kill the process immediately.
  73  *
  74  * Did I mention that signals suck?  At least in POSIX-compliant systems
  75  * they suck far less, as those systems have "sigaction()".
  76  */
  77 RETSIGTYPE
  78 (*setsignal (int sig, RETSIGTYPE (*func)(int)))(int)
  79 {
  80 #ifdef HAVE_SIGACTION
  81         struct sigaction old, new;
  82
  83         memset(&new, 0, sizeof(new));
  84         new.sa_handler = func;
  85         if (sigaction(sig, &new, &old) < 0)
  86                 return (SIG_ERR);
  87         return (old.sa_handler);
  88
  89 #else
  90 #ifdef HAVE_SIGSET
  91         return (sigset(sig, func));
  92 #else
  93         return (signal(sig, func));
  94 #endif
  95 #endif
  96 }
  97