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/*
* Copyright (C) 2004-2010 Andre Noll <maan@tuebingen.mpg.de>
*
* Licensed under the GPL v2. For licencing details see COPYING.
*/
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <dirent.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <stdlib.h>
#include <sys/select.h>
#include "gcc-compat.h"
#include "err.h"
#include "log.h"
#include "str.h"
#include "file.h"
#include "sig.h"
static int signal_pipe[2];
/**
* Initialize the signal subsystem.
*
* This function creates a pipe, the signal pipe, to deliver pending signals to
* the application (Bernstein's trick). It should be called during the
* application's startup part, followed by subsequent calls to
* install_sighandler() for each signal that should be caught.
*
* signal_init() installs a generic signal handler which is used for all
* signals simultaneously. When a signal arrives, this generic signal handler
* writes the corresponding signal number to the signal pipe so that the
* application can test for pending signals simply by checking the signal pipe
* for reading, e.g. by using the select(2) system call.
*
* \return This function either succeeds or calls exit(2) to terminate
* the current process. On success, the file descriptor of the signal pipe is
* returned.
*/
int signal_init(void)
{
int ret;
if (pipe(signal_pipe) < 0) {
ret = -ERRNO_TO_DSS_ERROR(errno);
goto err_out;
}
ret = mark_fd_nonblocking(signal_pipe[0]);
if (ret < 0)
goto err_out;
ret = mark_fd_nonblocking(signal_pipe[1]);
if (ret < 0)
goto err_out;
return signal_pipe[0];
err_out:
DSS_EMERG_LOG(("%s\n", dss_strerror(-ret)));
exit(EXIT_FAILURE);
}
/* Write the signal number to the signal pipe, abort on errors. */
static void generic_signal_handler(int s)
{
/*
* Signal handlers that make system calls must save a copy of errno on
* entry to the handler and restore it on exit, to prevent the
* possibility of overwriting a errno value that had previously been
* set in the main program.
*/
int save_errno = errno;
ssize_t ret = write(signal_pipe[1], &s, sizeof(int));
if (ret == sizeof(int)) {
errno = save_errno;
return;
}
if (ret < 0)
DSS_EMERG_LOG(("%s\n", strerror(errno)));
else
DSS_EMERG_LOG(("short write to signal pipe\n"));
exit(EXIT_FAILURE);
}
/**
* Reap one child.
*
* \param pid In case a child died, its pid is returned here.
*
* Call waitpid() and print a log message containing the pid and the cause of
* the child's death.
*
* \return A (negative) error code on errors, zero, if no child died, one
* otherwise. If and only if the function returns one, the content of \a pid is
* meaningful.
*
* \sa waitpid(2)
*/
int reap_child(pid_t *pid, int *status)
{
*pid = waitpid(-1, status, WNOHANG);
if (!*pid)
return 0;
if (*pid < 0)
return -ERRNO_TO_DSS_ERROR(errno);
if (WIFEXITED(*status))
DSS_DEBUG_LOG(("child %i exited. Exit status: %i\n", (int)*pid,
WEXITSTATUS(*status)));
else if (WIFSIGNALED(*status))
DSS_DEBUG_LOG(("child %i was killed by signal %i\n", (int)*pid,
WTERMSIG(*status)));
else
DSS_WARNING_LOG(("child %i terminated abormally\n", (int)*pid));
return 1;
}
/**
* Wrapper around signal(2)
*
* \param sig The number of the signal to catch.
*
* This installs the generic signal handler for the given signal.
*
* \return This function returns 1 on success and \p -E_SIGNAL_SIG_ERR on errors.
* \sa signal(2)
*/
int install_sighandler(int sig)
{
DSS_DEBUG_LOG(("catching signal %d\n", sig));
if (signal(sig, &generic_signal_handler) != SIG_ERR)
return 1;
return -E_SIGNAL_SIG_ERR;
}
/**
* Return number of next pending signal.
*
* This should be called if the fd for the signal pipe is ready for reading.
*
* \return On success, the number of the received signal is returned.
* If the read was interrupted by another signal the function returns 0.
* Otherwise a negative error code is returned.
*/
int next_signal(void)
{
int s, err;
ssize_t r;
r = read(signal_pipe[0], &s, sizeof(s));
if (r == sizeof(s)) {
DSS_DEBUG_LOG(("next signal: %d\n", s));
return s;
}
err = errno;
assert(r < 0);
if (err == EAGAIN)
return 0;
DSS_ERROR_LOG(("failed to read from signal pipe\n"));
return -ERRNO_TO_DSS_ERROR(err);
}
/**
* Close the signal pipe.
*/
void signal_shutdown(void)
{
close(signal_pipe[1]);
}
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