signal.c

   1 /*
   2  * Copyright (C) 2004-2008 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         write(signal_pipe[1], &s, sizeof(int));
  61         //fprintf(stderr, "got sig %i, write returned %d\n", s, ret);
  62 }
  63
  64 /**
  65  * Reap one child.
  66  *
  67  * \param pid In case a child died, its pid is returned here.
  68  *
  69  * Call waitpid() and print a log message containing the pid and the cause of
  70  * the child's death.
  71  *
  72  * \return A (negative) paraslash error code on errors, zero, if no child died,
  73  * one otherwise. If and only if the function returns one, the content of \a
  74  * pid is meaningful.
  75  *
  76  * \sa waitpid(2).
  77  */
  78 int para_reap_child(pid_t *pid)
  79 {
  80         int status;
  81         *pid = waitpid(-1, &status, WNOHANG);
  82
  83         if (!*pid)
  84                 return 0;
  85         if (*pid < 0)
  86                 return -ERRNO_TO_PARA_ERROR(errno);
  87         if (WIFEXITED(status))
  88                 PARA_DEBUG_LOG("child %i exited. Exit status: %i\n", (int)*pid,
  89                         WEXITSTATUS(status));
  90         else if (WIFSIGNALED(status))
  91                 PARA_DEBUG_LOG("child %i was killed by signal %i\n", (int)*pid,
  92                         WTERMSIG(status));
  93         else
  94                 PARA_WARNING_LOG("child %i terminated abormally\n", (int)*pid);
  95         return 1;
  96 }
  97
  98 /**
  99  * Paraslash's zombie killer.
 100  *
 101  * It just calls \p para_reap_child() until there are no more children left to
 102  * reap.
 103  */
 104 void para_reap_children(void)
 105 {
 106         pid_t pid;
 107
 108         while (para_reap_child(&pid) > 0)
 109                 ; /* nothing */
 110 }
 111
 112 /**
 113  * Wrapper around signal(2).
 114  *
 115  * \param sig The number of the signal to catch.
 116  *
 117  * This installs the generic signal handler for the given signal.
 118  *
 119  * \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on errors.
 120  *
 121  * \sa signal(2).
 122  */
 123 int para_install_sighandler(int sig)
 124 {
 125         PARA_DEBUG_LOG("catching signal %d\n", sig);
 126         return signal(sig, &generic_signal_handler) == SIG_ERR?  -E_SIGNAL_SIG_ERR : 1;
 127 }
 128
 129 /**
 130  * Return the number of next pending signal.
 131  *
 132  * This should be called if the fd for the signal pipe is ready for reading.
 133  *
 134  * \return On success, the number of the received signal is returned.  If the
 135  * read returned zero or was interrupted by another signal the function returns
 136  * 0.  Otherwise, a negative error value is returned.
 137  */
 138 int para_next_signal(void)
 139 {
 140         int s;
 141         ssize_t r = read(signal_pipe[0], &s, sizeof(s));
 142
 143         if (!r) {
 144                 PARA_CRIT_LOG("read from signal pipe returned zero\n");
 145                 return 0;
 146         }
 147         if (r < 0) {
 148                 if (errno == EAGAIN || errno == EINTR)
 149                         return 0;
 150                 return -ERRNO_TO_PARA_ERROR(errno);
 151         }
 152         assert(r == sizeof(s));
 153         PARA_DEBUG_LOG("next signal: %d\n", s);
 154         return s;
 155 }
 156
 157 /**
 158  * Close the write end of the signal pipe.
 159  */
 160 void para_signal_shutdown(void)
 161 {
 162         close(signal_pipe[1]);
 163 }