LXR busybox/networking/udhcp/signalpipe.c

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