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