lib/signals.c

   1 /*
   2  * Copyright (c) 2008, 2009 Nicira Networks.
   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 <unistd.h>
  24 #include "poll-loop.h"
  25 #include "socket-util.h"
  26 #include "util.h"
  27
  28 #if defined(_NSIG)
  29 #define N_SIGNALS _NSIG
  30 #elif defined(NSIG)
  31 #define N_SIGNALS NSIG
  32 #else
  33 /* We could try harder to get the maximum signal number, but in practice we
  34  * only care about SIGHUP, which is normally signal 1 anyway. */
  35 #define N_SIGNALS 32
  36 #endif
  37
  38 struct signal {
  39     int signr;
  40 };
  41
  42 static volatile sig_atomic_t signaled[N_SIGNALS];
  43
  44 static int fds[2];
  45
  46 static void signal_handler(int signr);
  47
  48 /* Initializes the signals subsystem (if it is not already initialized).  Calls
  49  * exit() if initialization fails.
  50  *
  51  * Calling this function is optional; it will be called automatically by
  52  * signal_start() if necessary.  Calling it explicitly allows the client to
  53  * prevent the process from exiting at an unexpected time. */
  54 void
  55 signal_init(void)
  56 {
  57     static bool inited;
  58     if (!inited) {
  59         inited = true;
  60         if (pipe(fds)) {
  61             ovs_fatal(errno, "could not create pipe");
  62         }
  63         set_nonblocking(fds[0]);
  64         set_nonblocking(fds[1]);
  65     }
  66 }
  67
  68 /* Sets up a handler for 'signr' and returns a structure that represents it.
  69  *
  70  * Only one handler for a given signal may be registered at a time. */
  71 struct signal *
  72 signal_register(int signr)
  73 {
  74     struct sigaction sa;
  75     struct signal *s;
  76
  77     signal_init();
  78
  79     /* Set up signal handler. */
  80     assert(signr >= 1 && signr < N_SIGNALS);
  81     memset(&sa, 0, sizeof sa);
  82     sa.sa_handler = signal_handler;
  83     sigemptyset(&sa.sa_mask);
  84     sa.sa_flags = SA_RESTART;
  85     if (sigaction(signr, &sa, NULL)) {
  86         ovs_fatal(errno, "sigaction(%d) failed", signr);
  87     }
  88
  89     /* Return structure. */
  90     s = xmalloc(sizeof *s);
  91     s->signr = signr;
  92     return s;
  93 }
  94
  95 /* Returns true if signal 's' has been received since the last call to this
  96  * function with argument 's'. */
  97 bool
  98 signal_poll(struct signal *s)
  99 {
 100     char buf[_POSIX_PIPE_BUF];
 101     ignore(read(fds[0], buf, sizeof buf));
 102     if (signaled[s->signr]) {
 103         signaled[s->signr] = 0;
 104         return true;
 105     }
 106     return false;
 107 }
 108
 109 /* Causes the next call to poll_block() to wake up when signal_poll(s) would
 110  * return true. */
 111 void
 112 signal_wait(struct signal *s)
 113 {
 114     if (signaled[s->signr]) {
 115         poll_immediate_wake();
 116     } else {
 117         poll_fd_wait(fds[0], POLLIN);
 118     }
 119 }
 120 \f
 121 static void
 122 signal_handler(int signr)
 123 {
 124     if (signr >= 1 && signr < N_SIGNALS) {
 125         ignore(write(fds[1], "", 1));
 126         signaled[signr] = true;
 127     }
 128 }