xref: /aosp_15_r20/external/libfuse/lib/fuse_signals.c (revision 9e5649576b786774a32d7b0252c9cd8c6538fa49)

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2007  Miklos Szeredi <[email protected]>

  Utility functions for setting signal handlers.

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

#include "fuse_config.h"
#include "fuse_lowlevel.h"
#include "fuse_i.h"

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

static struct fuse_session *fuse_instance;

static void dump_stack(void)
{
#ifdef HAVE_BACKTRACE
	const size_t backtrace_sz = 1024 * 1024;
	void* backtrace_buffer[backtrace_sz];

	int err_fd = fileno(stderr);

	int trace_len = backtrace(backtrace_buffer, backtrace_sz);
	backtrace_symbols_fd(backtrace_buffer, trace_len, err_fd);
#endif
}

static void exit_handler(int sig)
{
	if (fuse_instance) {
		fuse_session_exit(fuse_instance);
		if(sig <= 0) {
			fuse_log(FUSE_LOG_ERR, "assertion error: signal value <= 0\n");
			dump_stack();
			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)
		fuse_log(FUSE_LOG_ERR,
			"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);
}