fuse_signals.c

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2007  Miklos Szeredi <miklos@szeredi.hu>

  Utility functions for setting signal handlers.

  This program can be distributed under the terms of the GNU LGPLv2.
  See the file COPYING.LIB
*/

#include "config.h"
#include "fuse_lowlevel.h"
#include "fuse_i.h"

#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <stdlib.h>

static struct fuse_session *fuse_instance;

static void exit_handler(int sig)
{
        if (fuse_instance) {
                fuse_session_exit(fuse_instance);
                if(sig <= 0) {
                        fprintf(stderr, "assertion error: signal value <= 0\n");
                        abort();
                }
                fuse_instance->error = sig;
        }
}

static void do_nothing(int sig)
{
        (void) sig;
}

static int set_one_signal_handler(int sig, void (*handler)(int), int remove)
{
        struct sigaction sa;
        struct sigaction old_sa;

        memset(&sa, 0, sizeof(struct sigaction));
        sa.sa_handler = remove ? SIG_DFL : handler;
        sigemptyset(&(sa.sa_mask));
        sa.sa_flags = 0;

        if (sigaction(sig, NULL, &old_sa) == -1) {
                perror("fuse: cannot get old signal handler");
                return -1;
        }

        if (old_sa.sa_handler == (remove ? handler : SIG_DFL) &&
            sigaction(sig, &sa, NULL) == -1) {
                perror("fuse: cannot set signal handler");
                return -1;
        }
        return 0;
}

int fuse_set_signal_handlers(struct fuse_session *se)
{
        /* If we used SIG_IGN instead of the do_nothing function,
           then we would be unable to tell if we set SIG_IGN (and
           thus should reset to SIG_DFL in fuse_remove_signal_handlers)
           or if it was already set to SIG_IGN (and should be left
           untouched. */
        if (set_one_signal_handler(SIGHUP, exit_handler, 0) == -1 ||
            set_one_signal_handler(SIGINT, exit_handler, 0) == -1 ||
            set_one_signal_handler(SIGTERM, exit_handler, 0) == -1 ||
            set_one_signal_handler(SIGPIPE, do_nothing, 0) == -1)
                return -1;

        fuse_instance = se;
        return 0;
}

void fuse_remove_signal_handlers(struct fuse_session *se)
{
        if (fuse_instance != se)
                fprintf(stderr,
                        "fuse: fuse_remove_signal_handlers: unknown session\n");
        else
                fuse_instance = NULL;

        set_one_signal_handler(SIGHUP, exit_handler, 1);
        set_one_signal_handler(SIGINT, exit_handler, 1);
        set_one_signal_handler(SIGTERM, exit_handler, 1);
        set_one_signal_handler(SIGPIPE, do_nothing, 1);
}