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  * Paraslash's zombie killer.
 107  *
 108  * It just calls \p para_reap_child() until there are no more children left to
 109  * reap.
 110  */
 111 void para_reap_children(void)
 112 {
 113         pid_t pid;
 114
 115         while (para_reap_child(&pid) > 0)
 116                 ; /* nothing */
 117 }
 118
 119 /**
 120  * Install the given handler for the given signal.
 121  *
 122  * \param sig The number of the signal to catch.
 123  * \param handler to be installed, \p SIG_IGN, or \p SIG_DFL.
 124  *
 125  * \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on
 126  * errors.
 127  *
 128  * \sa sigaction(2).
 129  */
 130 int para_sigaction(int sig, void (*handler)(int))
 131 {
 132         struct sigaction act;
 133
 134         PARA_DEBUG_LOG("catching signal %d\n", sig);
 135         act.sa_handler = handler;
 136         sigemptyset(&act.sa_mask);
 137         act.sa_flags = 0;
 138         if (sig == SIGALRM) {
 139                 #ifdef SA_INTERRUPT /* SunOS */
 140                         act.sa_flags |= SA_INTERRUPT;
 141                 #endif
 142         } else {
 143                 #ifdef SA_RESTART /* BSD */
 144                         act.sa_flags |= SA_RESTART;
 145                 #endif
 146         }
 147         if (sigaction(sig, &act, NULL) < 0)
 148                 return -E_SIGNAL_SIG_ERR;
 149         return 1;
 150 }
 151
 152 /**
 153  * Install the generic signal handler for the given signal number.
 154  *
 155  * \param sig The number of the signal to catch.
 156  *
 157  * \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on
 158  * errors.
 159  *
 160  * \sa signal(2), sigaction(2).
 161  */
 162 int para_install_sighandler(int sig)
 163 {
 164         return para_sigaction(sig, &generic_signal_handler);
 165 }
 166
 167 /**
 168  * Return the number of next pending signal.
 169  *
 170  * This should be called if the fd for the signal pipe is ready for reading.
 171  *
 172  * \return On success, the number of the received signal is returned.  If the
 173  * read returned zero or was interrupted by another signal the function returns
 174  * 0.  Otherwise, a negative error value is returned.
 175  */
 176 int para_next_signal(void)
 177 {
 178         int s;
 179         ssize_t r = read(signal_pipe[0], &s, sizeof(s));
 180
 181         if (!r) {
 182                 PARA_CRIT_LOG("read from signal pipe returned zero\n");
 183                 return 0;
 184         }
 185         if (r < 0) {
 186                 if (errno == EAGAIN || errno == EINTR)
 187                         return 0;
 188                 return -ERRNO_TO_PARA_ERROR(errno);
 189         }
 190         assert(r == sizeof(s));
 191         PARA_DEBUG_LOG("next signal: %d\n", s);
 192         return s;
 193 }
 194
 195 /**
 196  * Close the write end of the signal pipe.
 197  */
 198 void para_signal_shutdown(void)
 199 {
 200         close(signal_pipe[1]);
 201 }