signal.c

   1 /*
   2  * Copyright (C) 2004-2013 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
  11 #include "para.h"
  12 #include "error.h"
  13 #include "fd.h"
  14 #include "list.h"
  15 #include "sched.h"
  16 #include "signal.h"
  17
  18 static int signal_pipe[2];
  19
  20 /**
  21  * Initialize the paraslash signal subsystem.
  22  *
  23  * This function creates a pipe, the signal pipe, to deliver pending
  24  * signals to the application (Bernstein's trick). It should be called
  25  * during the application's startup part, followed by subsequent calls
  26  * to para_install_sighandler() for each signal that should be caught.
  27  *
  28  * A generic signal handler is used for all signals simultaneously. When a
  29  * signal arrives, the signal handler writes the number of the signal received
  30  * to one end of the signal pipe. The application can test for pending signals
  31  * by checking if the file descriptor of the other end of the signal pipe is
  32  * ready for reading, see select(2).
  33  *
  34  * \return This function either succeeds or calls exit(2) to terminate the
  35  * current process. On success, the file descriptor of the read end of the
  36  * signal pipe is returned.
  37  */
  38 int para_signal_init(void)
  39 {
  40         int ret;
  41         if (pipe(signal_pipe) < 0) {
  42                 ret = -ERRNO_TO_PARA_ERROR(errno);
  43                 goto err_out;
  44         }
  45         ret = mark_fd_nonblocking(signal_pipe[0]);
  46         if (ret < 0)
  47                 goto err_out;
  48         ret = mark_fd_nonblocking(signal_pipe[1]);
  49         if (ret < 0)
  50                 goto err_out;
  51         return signal_pipe[0];
  52 err_out:
  53         PARA_EMERG_LOG("%s\n", para_strerror(-ret));
  54         exit(EXIT_FAILURE);
  55 }
  56
  57 /* Write the signal number to signal pipe. */
  58 static void generic_signal_handler(int s)
  59 {
  60         /*
  61          * Signal handlers that make system calls must save a copy of errno on
  62          * entry to the handler and restore it on exit, to prevent the
  63          * possibility of overwriting a errno value that had previously been
  64          * set in the main program.
  65          */
  66         int save_errno = errno;
  67         ssize_t ret = write(signal_pipe[1], &s, sizeof(int));
  68
  69         if (ret == sizeof(int)) {
  70                 errno = save_errno;
  71                 return;
  72         }
  73         if (ret < 0)
  74                 PARA_EMERG_LOG("%s\n", strerror(errno));
  75         else
  76                 PARA_EMERG_LOG("short write to signal pipe\n");
  77         exit(EXIT_FAILURE);
  78 }
  79
  80 /**
  81  * Reap one child.
  82  *
  83  * \param pid In case a child died, its pid is returned here.
  84  *
  85  * Call waitpid() and print a log message containing the pid and the cause of
  86  * the child's death.
  87  *
  88  * \return A (negative) paraslash error code on errors, zero, if no child died,
  89  * one otherwise. If and only if the function returns one, the content of \a
  90  * pid is meaningful.
  91  *
  92  * \sa waitpid(2).
  93  */
  94 int para_reap_child(pid_t *pid)
  95 {
  96         int status;
  97         *pid = waitpid(-1, &status, WNOHANG);
  98
  99         if (!*pid)
 100                 return 0;
 101         if (*pid < 0)
 102                 return -ERRNO_TO_PARA_ERROR(errno);
 103         if (WIFEXITED(status))
 104                 PARA_DEBUG_LOG("child %i exited. Exit status: %i\n", (int)*pid,
 105                         WEXITSTATUS(status));
 106         else if (WIFSIGNALED(status))
 107                 PARA_DEBUG_LOG("child %i was killed by signal %i\n", (int)*pid,
 108                         WTERMSIG(status));
 109         else
 110                 PARA_WARNING_LOG("child %i terminated abormally\n", (int)*pid);
 111         return 1;
 112 }
 113
 114 /**
 115  * Install the given handler for the given signal.
 116  *
 117  * \param sig The number of the signal to catch.
 118  * \param handler to be installed, \p SIG_IGN, or \p SIG_DFL.
 119  *
 120  * This either succeeds or calls exit(EXIT_FAILURE).
 121  *
 122  * \sa sigaction(2).
 123  */
 124 void para_sigaction(int sig, void (*handler)(int))
 125 {
 126         struct sigaction act;
 127
 128         PARA_DEBUG_LOG("catching signal %d\n", sig);
 129         act.sa_handler = handler;
 130         sigemptyset(&act.sa_mask);
 131         act.sa_flags = 0;
 132         if (sig == SIGALRM) {
 133                 #ifdef SA_INTERRUPT /* SunOS */
 134                         act.sa_flags |= SA_INTERRUPT;
 135                 #endif
 136         } else {
 137                 #ifdef SA_RESTART /* BSD */
 138                         act.sa_flags |= SA_RESTART;
 139                 #endif
 140         }
 141         if (sigaction(sig, &act, NULL) >= 0)
 142                 return;
 143         PARA_EMERG_LOG("failed to install signal handler for signal %d\n",
 144                 sig);
 145         exit(EXIT_FAILURE);
 146 }
 147
 148 /**
 149  * Install the generic signal handler for the given signal number.
 150  *
 151  * \param sig The number of the signal to catch.
 152  *
 153  * \sa signal(2), sigaction(2).
 154  */
 155 void para_install_sighandler(int sig)
 156 {
 157         para_sigaction(sig, &generic_signal_handler);
 158 }
 159
 160 /**
 161  * Block a signal for the caller.
 162  *
 163  * \param sig The signal to block.
 164  *
 165  * This sets the given signal in the current signal mask of the calling process
 166  * to prevent this signal from delivery.
 167  *
 168  * \sa \ref para_unblock_signal(), sigprocmask(2), sigaddset(3).
 169  */
 170 void para_block_signal(int sig)
 171 {
 172         sigset_t set;
 173
 174         PARA_DEBUG_LOG("blocking signal %d\n", sig);
 175         sigemptyset(&set);
 176         sigaddset(&set, sig);
 177         sigprocmask(SIG_BLOCK, &set, NULL);
 178 }
 179
 180 /**
 181  * Unblock a signal.
 182  *
 183  * \param sig The signal to unblock.
 184  *
 185  * This function removes the given signal from the current set of blocked
 186  * signals.
 187  *
 188  * \sa \ref para_block_signal(), sigprocmask(2), sigaddset(3).
 189  */
 190 void para_unblock_signal(int sig)
 191 {
 192         sigset_t set;
 193
 194         PARA_DEBUG_LOG("unblocking signal %d\n", sig);
 195         sigemptyset(&set);
 196         sigaddset(&set, sig);
 197         sigprocmask(SIG_UNBLOCK, &set, NULL);
 198 }
 199
 200 /**
 201  * Return the number of the next pending signal.
 202  *
 203  * \param rfds The fd_set containing the signal pipe.
 204  *
 205  * \return On success, the number of the received signal is returned. If there
 206  * is no signal currently pending, the function returns zero. On read errors
 207  * from the signal pipe, the process is terminated.
 208  */
 209 int para_next_signal(fd_set *rfds)
 210 {
 211         size_t n;
 212         int s, ret = read_nonblock(signal_pipe[0], &s, sizeof(s), rfds, &n);
 213
 214         if (ret < 0) {
 215                 PARA_EMERG_LOG("%s\n", para_strerror(-ret));
 216                 exit(EXIT_FAILURE);
 217         }
 218         if (n == 0)
 219                 return 0;
 220         assert(n == sizeof(s));
 221         PARA_DEBUG_LOG("next signal: %d\n", s);
 222         return s;
 223 }
 224
 225 /**
 226  * Close the write end of the signal pipe.
 227  */
 228 void para_signal_shutdown(void)
 229 {
 230         close(signal_pipe[1]);
 231 }