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