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 <assert.h>
  20 #include <errno.h>
  21 #include <limits.h>
  22 #include <signal.h>
  23 #include <stdlib.h>
  24 #include <unistd.h>
  25 #include "poll-loop.h"
  26 #include "socket-util.h"
  27 #include "type-props.h"
  28 #include "util.h"
  29 #include "vlog.h"
  30
  31 VLOG_DEFINE_THIS_MODULE(signals);
  32
  33 #if defined(_NSIG)
  34 #define N_SIGNALS _NSIG
  35 #elif defined(NSIG)
  36 #define N_SIGNALS NSIG
  37 #else
  38 /* We could try harder to get the maximum signal number, but in practice we
  39  * only care about SIGHUP, which is normally signal 1 anyway. */
  40 #define N_SIGNALS 32
  41 #endif
  42
  43 struct signal {
  44     struct sigaction saved_sa;
  45     int signr;
  46 };
  47
  48 static volatile sig_atomic_t signaled[N_SIGNALS];
  49
  50 static int fds[2];
  51
  52 static void signal_handler(int signr);
  53
  54 /* Initializes the signals subsystem (if it is not already initialized).  Calls
  55  * exit() if initialization fails.
  56  *
  57  * Calling this function is optional; it will be called automatically by
  58  * signal_start() if necessary.  Calling it explicitly allows the client to
  59  * prevent the process from exiting at an unexpected time. */
  60 void
  61 signal_init(void)
  62 {
  63     static bool inited;
  64     if (!inited) {
  65         inited = true;
  66         xpipe_nonblocking(fds);
  67     }
  68 }
  69
  70 /* Sets up a handler for 'signr' and returns a structure that represents it.
  71  *
  72  * Only one handler for a given signal may be registered at a time. */
  73 struct signal *
  74 signal_register(int signr)
  75 {
  76     struct sigaction sa;
  77     struct signal *s;
  78
  79     signal_init();
  80
  81     s = xmalloc(sizeof *s);
  82     s->signr = signr;
  83
  84     /* Set up signal handler. */
  85     assert(signr >= 1 && signr < N_SIGNALS);
  86     memset(&sa, 0, sizeof sa);
  87     sa.sa_handler = signal_handler;
  88     sigemptyset(&sa.sa_mask);
  89     sa.sa_flags = SA_RESTART;
  90     xsigaction(signr, &sa, &s->saved_sa);
  91
  92     return s;
  93 }
  94
  95 /* Unregisters the handler for 's', restores the signal handler that was in
  96  * effect before signal_register() was called, and frees 's'. */
  97 void
  98 signal_unregister(struct signal *s)
  99 {
 100     if (s) {
 101         xsigaction(s->signr, &s->saved_sa, NULL);
 102         free(s);
 103     }
 104 }
 105
 106 /* Returns true if signal 's' has been received since the last call to this
 107  * function with argument 's'. */
 108 bool
 109 signal_poll(struct signal *s)
 110 {
 111     char buf[_POSIX_PIPE_BUF];
 112     ignore(read(fds[0], buf, sizeof buf));
 113     if (signaled[s->signr]) {
 114         signaled[s->signr] = 0;
 115         return true;
 116     }
 117     return false;
 118 }
 119
 120 /* Causes the next call to poll_block() to wake up when signal_poll(s) would
 121  * return true. */
 122 void
 123 signal_wait(struct signal *s)
 124 {
 125     if (signaled[s->signr]) {
 126         poll_immediate_wake();
 127     } else {
 128         poll_fd_wait(fds[0], POLLIN);
 129     }
 130 }
 131 \f
 132 static void
 133 signal_handler(int signr)
 134 {
 135     if (signr >= 1 && signr < N_SIGNALS) {
 136         ignore(write(fds[1], "", 1));
 137         signaled[signr] = true;
 138     }
 139 }
 140
 141 /* Returns the name of signal 'signum' as a string.  The string may be in a
 142  * static buffer that is reused from one call to the next.
 143  *
 144  * The string is probably a (possibly multi-word) description of the signal
 145  * (e.g. "Hangup") instead of just the stringified version of the macro
 146  * (e.g. "SIGHUP"). */
 147 const char *
 148 signal_name(int signum)
 149 {
 150     const char *name = NULL;
 151 #ifdef HAVE_STRSIGNAL
 152     name = strsignal(signum);
 153 #endif
 154     if (!name) {
 155         static char buffer[7 + INT_STRLEN(int) + 1];
 156         sprintf(buffer, "signal %d", signum);
 157         name = buffer;
 158     }
 159     return name;
 160 }
 161
 162 void
 163 xsigaction(int signum, const struct sigaction *new, struct sigaction *old)
 164 {
 165     if (sigaction(signum, new, old)) {
 166         VLOG_FATAL("sigaction(%s) failed (%s)",
 167                    signal_name(signum), strerror(errno));
 168     }
 169 }
 170
 171 void
 172 xsigprocmask(int how, const sigset_t *new, sigset_t *old)
 173 {
 174     if (sigprocmask(how, new, old)) {
 175         VLOG_FATAL("sigprocmask failed (%s)", strerror(errno));
 176     }
 177 }