signal.c

   1 /*
   2  * Copyright (C) 2004-2009 Andre Noll <maan@systemlinux.org>
   3  *
   4  * Licensed under the GPL v2. For licencing details see COPYING.
   5  */
   6 /** \file signal.c Signal handling functions. */
   7
   8 #include <signal.h>
   9 #include <sys/types.h>
  10 #include <dirent.h>
  11
  12 #include "para.h"
  13 #include "error.h"
  14 #include "fd.h"
  15
  16 static int signal_pipe[2];
  17
  18 /**
  19  * Initialize the paraslash signal subsystem.
  20  *
  21  * This function creates a pipe, the signal pipe, to deliver pending
  22  * signals to the application (Bernstein's trick). It should be called
  23  * during the application's startup part, followed by subsequent calls
  24  * to para_install_sighandler() for each signal that should be caught.
  25  *
  26  * para_signal_init() installs a generic signal handler which is used for all
  27  * signals simultaneously. When a signal arrives, this generic signal handler
  28  * writes the corresponding signal number to the signal pipe so that the
  29  * application can test for pending signals simply by checking the signal pipe
  30  * for reading, e.g. by using the select(2) system call.
  31  *
  32  * \return This function either succeeds or calls exit(2) to terminate
  33  * the current process. On success, the file descriptor of the signal pipe is
  34  * returned.
  35  */
  36 int para_signal_init(void)
  37 {
  38         int ret;
  39         if (pipe(signal_pipe) < 0) {
  40                 ret = -ERRNO_TO_PARA_ERROR(errno);
  41                 goto err_out;
  42         }
  43         ret = mark_fd_nonblocking(signal_pipe[0]);
  44         if (ret < 0)
  45                 goto err_out;
  46         ret = mark_fd_nonblocking(signal_pipe[1]);
  47         if (ret < 0)
  48                 goto err_out;
  49         return signal_pipe[0];
  50 err_out:
  51         PARA_EMERG_LOG("%s\n", para_strerror(-ret));
  52         exit(EXIT_FAILURE);
  53 }
  54
  55 /*
  56  * just write one integer to signal pipe
  57  */
  58 static void generic_signal_handler(int s)
  59 {
  60         ssize_t ret = write(signal_pipe[1], &s, sizeof(int));
  61
  62         if (ret == sizeof(int))
  63                 return;
  64         if (ret < 0)
  65                 PARA_EMERG_LOG("%s\n", strerror(errno));
  66         else
  67                 PARA_EMERG_LOG("short write to signal pipe\n");
  68         exit(EXIT_FAILURE);
  69 }
  70
  71 /**
  72  * Reap one child.
  73  *
  74  * \param pid In case a child died, its pid is returned here.
  75  *
  76  * Call waitpid() and print a log message containing the pid and the cause of
  77  * the child's death.
  78  *
  79  * \return A (negative) paraslash error code on errors, zero, if no child died,
  80  * one otherwise. If and only if the function returns one, the content of \a
  81  * pid is meaningful.
  82  *
  83  * \sa waitpid(2).
  84  */
  85 int para_reap_child(pid_t *pid)
  86 {
  87         int status;
  88         *pid = waitpid(-1, &status, WNOHANG);
  89
  90         if (!*pid)
  91                 return 0;
  92         if (*pid < 0)
  93                 return -ERRNO_TO_PARA_ERROR(errno);
  94         if (WIFEXITED(status))
  95                 PARA_DEBUG_LOG("child %i exited. Exit status: %i\n", (int)*pid,
  96                         WEXITSTATUS(status));
  97         else if (WIFSIGNALED(status))
  98                 PARA_DEBUG_LOG("child %i was killed by signal %i\n", (int)*pid,
  99                         WTERMSIG(status));
 100         else
 101                 PARA_WARNING_LOG("child %i terminated abormally\n", (int)*pid);
 102         return 1;
 103 }
 104
 105 /**
 106  * Install the given handler for the given signal.
 107  *
 108  * \param sig The number of the signal to catch.
 109  * \param handler to be installed, \p SIG_IGN, or \p SIG_DFL.
 110  *
 111  * This either succeeds or calls exit(EXIT_FAILURE).
 112  *
 113  * \sa sigaction(2).
 114  */
 115 void para_sigaction(int sig, void (*handler)(int))
 116 {
 117         struct sigaction act;
 118
 119         PARA_DEBUG_LOG("catching signal %d\n", sig);
 120         act.sa_handler = handler;
 121         sigemptyset(&act.sa_mask);
 122         act.sa_flags = 0;
 123         if (sig == SIGALRM) {
 124                 #ifdef SA_INTERRUPT /* SunOS */
 125                         act.sa_flags |= SA_INTERRUPT;
 126                 #endif
 127         } else {
 128                 #ifdef SA_RESTART /* BSD */
 129                         act.sa_flags |= SA_RESTART;
 130                 #endif
 131         }
 132         if (sigaction(sig, &act, NULL) >= 0)
 133                 return;
 134         PARA_EMERG_LOG("failed to install signal handler for signal %d\n",
 135                 sig);
 136         exit(EXIT_FAILURE);
 137 }
 138
 139 /**
 140  * Install the generic signal handler for the given signal number.
 141  *
 142  * \param sig The number of the signal to catch.
 143  *
 144  * \sa signal(2), sigaction(2).
 145  */
 146 void para_install_sighandler(int sig)
 147 {
 148         para_sigaction(sig, &generic_signal_handler);
 149 }
 150
 151 /**
 152  * Return the number of the next pending signal.
 153  *
 154  * This should be called if the fd for the signal pipe is ready for reading.
 155  *
 156  * \return On success, the number of the received signal is returned.  If the
 157  * read returned zero or was interrupted by another signal the function returns
 158  * 0.  Otherwise, a negative error value is returned.
 159  */
 160 int para_next_signal(void)
 161 {
 162         int s;
 163         ssize_t r = read(signal_pipe[0], &s, sizeof(s));
 164
 165         if (!r) {
 166                 PARA_CRIT_LOG("read from signal pipe returned zero\n");
 167                 return 0;
 168         }
 169         if (r < 0) {
 170                 if (errno == EAGAIN || errno == EINTR)
 171                         return 0;
 172                 return -ERRNO_TO_PARA_ERROR(errno);
 173         }
 174         assert(r == sizeof(s));
 175         PARA_DEBUG_LOG("next signal: %d\n", s);
 176         return s;
 177 }
 178
 179 /**
 180  * Close the write end of the signal pipe.
 181  */
 182 void para_signal_shutdown(void)
 183 {
 184         close(signal_pipe[1]);
 185 }