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 #ifdef HAVE_CONFIG_H
  23 #include "config.h"
  24 #endif
  25
  26 #include <netdissect-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