1/* vi: set sw=4 ts=4: */
2/* signalpipe.c
3 *
4 * Signal pipe infrastructure. A reliable way of delivering signals.
5 *
6 * Russ Dill <Russ.Dill@asu.edu> December 2003
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation; either version 2 of the License, or
11 * (at your option) any later version.
12 *
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
16 * GNU General Public License for more details.
17 *
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
21 */
22
23#include "common.h"
24
25
26static int signal_pipe[2];
27
28static void signal_handler(int sig)
29{
30	unsigned char ch = sig; /* use char, avoid dealing with partial writes */
31	if (write(signal_pipe[1], &ch, 1) != 1)
32		bb_perror_msg("cannot send signal");
33}
34
35
36/* Call this before doing anything else. Sets up the socket pair
37 * and installs the signal handler */
38void udhcp_sp_setup(void)
39{
40	/* was socketpair, but it needs AF_UNIX in kernel */
41	xpipe(signal_pipe);
42	fcntl(signal_pipe[0], F_SETFD, FD_CLOEXEC);
43	fcntl(signal_pipe[1], F_SETFD, FD_CLOEXEC);
44	fcntl(signal_pipe[1], F_SETFL, O_NONBLOCK);
45	signal(SIGUSR1, signal_handler);
46	signal(SIGUSR2, signal_handler);
47	signal(SIGTERM, signal_handler);
48}
49
50
51/* Quick little function to setup the rfds. Will return the
52 * max_fd for use with select. Limited in that you can only pass
53 * one extra fd */
54int udhcp_sp_fd_set(fd_set *rfds, int extra_fd)
55{
56	FD_ZERO(rfds);
57	FD_SET(signal_pipe[0], rfds);
58	if (extra_fd >= 0) {
59		fcntl(extra_fd, F_SETFD, FD_CLOEXEC);
60		FD_SET(extra_fd, rfds);
61	}
62	return signal_pipe[0] > extra_fd ? signal_pipe[0] : extra_fd;
63}
64
65
66/* Read a signal from the signal pipe. Returns 0 if there is
67 * no signal, -1 on error (and sets errno appropriately), and
68 * your signal on success */
69int udhcp_sp_read(fd_set *rfds)
70{
71	unsigned char sig;
72
73	if (!FD_ISSET(signal_pipe[0], rfds))
74		return 0;
75
76	if (read(signal_pipe[0], &sig, 1) != 1)
77		return -1;
78
79	return sig;
80}
81