signal.c

   1 /*
   2  * Copyright (C) 2004-2006 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_nonblock(signal_pipe[0]);
  44         if (ret < 0)
  45                 goto err_out;
  46         ret = mark_fd_nonblock(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  * call waitpid() and print a log message containing the pid
  68  * and the cause of the child's death.
  69  *
  70  * \return Like \p waitpid(), this function returns the process ID of the
  71  * terminated child; on error, \p -E_WAITPID is returned.
  72  * \sa waitpid(2)
  73  */
  74 pid_t para_reap_child(void)
  75 {
  76         int status;
  77         pid_t pid = waitpid(-1, &status, WNOHANG);
  78
  79         if (pid <= 0) {
  80                 if (pid < 0)
  81                         pid = -E_WAITPID;
  82                 return pid;
  83         }
  84         if (WIFEXITED(status))
  85                 PARA_DEBUG_LOG("child %i exited. Exit status: %i\n", pid,
  86                         WEXITSTATUS(status));
  87         else if (WIFSIGNALED(status))
  88                 PARA_DEBUG_LOG("child %i was killed by signal %i\n", pid,
  89                         WTERMSIG(status));
  90         else
  91                 PARA_WARNING_LOG("child %i terminated abormally\n", pid);
  92         return pid;
  93 }
  94
  95 /**
  96  * paraslash's zombie killer
  97  *
  98  * It just calls \p para_reap_child() until there are no more children left to
  99  * reap.
 100  */
 101 void para_reap_children(void)
 102 {
 103         while (para_reap_child() > 0)
 104                 ; /* nothing */
 105 }
 106
 107 /**
 108  * wrapper around signal(2)
 109  * \param sig the number of the signal to catch
 110  *
 111  * This installs the generic signal handler for the given signal.
 112  * \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on errors.
 113  * \sa signal(2)
 114  */
 115 int para_install_sighandler(int sig)
 116 {
 117         PARA_DEBUG_LOG("catching signal %d\n", sig);
 118         return signal(sig, &generic_signal_handler) == SIG_ERR?  -E_SIGNAL_SIG_ERR : 1;
 119 }
 120
 121 /**
 122  * return number of next pending signal
 123  *
 124  * This should be called if the fd for the signal pipe is ready for reading.
 125  *
 126  * \return On success, the number of the received signal is returned. \p
 127  * -E_SIGNAL_READ is returned if a read error occurred while reading the signal
 128  * pipe.  If the read was interrupted by another signal the function returns 0.
 129  */
 130 int para_next_signal(void)
 131 {
 132         int s;
 133         ssize_t r;
 134
 135         if ((r = read(signal_pipe[0], &s, sizeof(s)) == sizeof(s)) > 0) {
 136                 PARA_DEBUG_LOG("next signal: %d\n", s);
 137                 return s;
 138         }
 139         return r < 0 && (errno != EAGAIN)? 0 : -E_SIGNAL_READ;
 140 }