lib/signals.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2011, 2012 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18 #include "signals.h"
  19 #include <errno.h>
  20 #include <limits.h>
  21 #include <signal.h>
  22 #include <stdlib.h>
  23 #include <unistd.h>
  24 #include "poll-loop.h"
  25 #include "socket-util.h"
  26 #include "type-props.h"
  27 #include "util.h"
  28 #include "vlog.h"
  29
  30 VLOG_DEFINE_THIS_MODULE(signals);
  31
  32 #if defined(_NSIG)
  33 #define N_SIGNALS _NSIG
  34 #elif defined(NSIG)
  35 #define N_SIGNALS NSIG
  36 #else
  37 /* We could try harder to get the maximum signal number, but in practice we
  38  * only care about SIGHUP, which is normally signal 1 anyway. */
  39 #define N_SIGNALS 32
  40 #endif
  41
  42 struct signal {
  43     struct sigaction saved_sa;
  44     int signr;
  45 };
  46
  47 static volatile sig_atomic_t signaled[N_SIGNALS];
  48
  49 static int fds[2];
  50
  51 static void signal_handler(int signr);
  52
  53 /* Initializes the signals subsystem (if it is not already initialized).  Calls
  54  * exit() if initialization fails.
  55  *
  56  * Calling this function is optional; it will be called automatically by
  57  * signal_start() if necessary.  Calling it explicitly allows the client to
  58  * prevent the process from exiting at an unexpected time. */
  59 void
  60 signal_init(void)
  61 {
  62     static bool inited;
  63     if (!inited) {
  64         inited = true;
  65         xpipe_nonblocking(fds);
  66     }
  67 }
  68
  69 /* Sets up a handler for 'signr' and returns a structure that represents it.
  70  *
  71  * Only one handler for a given signal may be registered at a time. */
  72 struct signal *
  73 signal_register(int signr)
  74 {
  75     struct sigaction sa;
  76     struct signal *s;
  77
  78     signal_init();
  79
  80     s = xmalloc(sizeof *s);
  81     s->signr = signr;
  82
  83     /* Set up signal handler. */
  84     ovs_assert(signr >= 1 && signr < N_SIGNALS);
  85     memset(&sa, 0, sizeof sa);
  86     sa.sa_handler = signal_handler;
  87     sigemptyset(&sa.sa_mask);
  88     sa.sa_flags = SA_RESTART;
  89     xsigaction(signr, &sa, &s->saved_sa);
  90
  91     return s;
  92 }
  93
  94 /* Unregisters the handler for 's', restores the signal handler that was in
  95  * effect before signal_register() was called, and frees 's'. */
  96 void
  97 signal_unregister(struct signal *s)
  98 {
  99     if (s) {
 100         xsigaction(s->signr, &s->saved_sa, NULL);
 101         free(s);
 102     }
 103 }
 104
 105 /* Returns true if signal 's' has been received since the last call to this
 106  * function with argument 's'. */
 107 bool
 108 signal_poll(struct signal *s)
 109 {
 110     char buf[_POSIX_PIPE_BUF];
 111     ignore(read(fds[0], buf, sizeof buf));
 112     if (signaled[s->signr]) {
 113         signaled[s->signr] = 0;
 114         return true;
 115     }
 116     return false;
 117 }
 118
 119 /* Causes the next call to poll_block() to wake up when signal_poll(s) would
 120  * return true. */
 121 void
 122 signal_wait(struct signal *s)
 123 {
 124     if (signaled[s->signr]) {
 125         poll_immediate_wake();
 126     } else {
 127         poll_fd_wait(fds[0], POLLIN);
 128     }
 129 }
 130 \f
 131 static void
 132 signal_handler(int signr)
 133 {
 134     if (signr >= 1 && signr < N_SIGNALS) {
 135         ignore(write(fds[1], "", 1));
 136         signaled[signr] = true;
 137     }
 138 }
 139
 140 /* Returns the name of signal 'signum' as a string.  The string may be in a
 141  * static buffer that is reused from one call to the next.
 142  *
 143  * The string is probably a (possibly multi-word) description of the signal
 144  * (e.g. "Hangup") instead of just the stringified version of the macro
 145  * (e.g. "SIGHUP"). */
 146 const char *
 147 signal_name(int signum)
 148 {
 149     const char *name = NULL;
 150 #ifdef HAVE_STRSIGNAL
 151     name = strsignal(signum);
 152 #endif
 153     if (!name) {
 154         static char buffer[7 + INT_STRLEN(int) + 1];
 155         sprintf(buffer, "signal %d", signum);
 156         name = buffer;
 157     }
 158     return name;
 159 }
 160
 161 void
 162 xsigaction(int signum, const struct sigaction *new, struct sigaction *old)
 163 {
 164     if (sigaction(signum, new, old)) {
 165         VLOG_FATAL("sigaction(%s) failed (%s)",
 166                    signal_name(signum), strerror(errno));
 167     }
 168 }
 169
 170 void
 171 xsigprocmask(int how, const sigset_t *new, sigset_t *old)
 172 {
 173     if (sigprocmask(how, new, old)) {
 174         VLOG_FATAL("sigprocmask failed (%s)", strerror(errno));
 175     }
 176 }