release/src/router/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 */
  24 static struct fd_pair signal_pipe;
  25
  26 static 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 */
  35 void 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 */
  52 int 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 */
  66 int 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 }