system.c 5.2 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186
/*
 * Licensed to the OpenAirInterface (OAI) Software Alliance under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The OpenAirInterface Software Alliance licenses this file to You under
 * the OAI Public License, Version 1.0  (the "License"); you may not use this file
 * except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.openairinterface.org/?page_id=698
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *-------------------------------------------------------------------------------
 * For more information about the OpenAirInterface (OAI) Software Alliance:
 *      contact@openairinterface.org
 */

/* This module provides a separate process to run system().
 * The communication between this process and the main processing
 * is done through unix pipes.
 *
 * Motivation: the UE sets its IP address using system() and
 * that disrupts realtime processing in some cases. Having a
 * separate process solves this problem.
 */

#include "system.h"
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <string.h>

#define MAX_COMMAND 4096

static int command_pipe_read;
static int command_pipe_write;
static int result_pipe_read;
static int result_pipe_write;

static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;

static int module_initialized = 0;

/********************************************************************/
/* util functions                                                   */
/********************************************************************/

static void lock_system(void)
{
  if (pthread_mutex_lock(&lock) != 0) {
    printf("pthread_mutex_lock fails\n");
    abort();
  }
}

static void unlock_system(void)
{
  if (pthread_mutex_unlock(&lock) != 0) {
    printf("pthread_mutex_unlock fails\n");
    abort();
  }
}

static void write_pipe(int p, char *b, int size)
{
  while (size) {
    int ret = write(p, b, size);
    if (ret <= 0) exit(0);
    b += ret;
    size -= ret;
  }
}

static void read_pipe(int p, char *b, int size)
{
  while (size) {
    int ret = read(p, b, size);
    if (ret <= 0) exit(0);
    b += ret;
    size -= ret;
  }
}

/********************************************************************/
/* background process                                               */
/********************************************************************/

/* This function is run by background process. It waits for a command,
 * runs it, and reports status back. It exits (in normal situations)
 * when the main process exits, because then a "read" on the pipe
 * will return 0, in which case "read_pipe" exits.
 */
static void background_system_process(void)
{
  int len;
  int ret;
  char command[MAX_COMMAND+1];

  while (1) {
    read_pipe(command_pipe_read, (char*)&len, sizeof(int));
    read_pipe(command_pipe_read, command, len);
    ret = system(command);
    write_pipe(result_pipe_write, (char *)&ret, sizeof(int));
  }
}

/********************************************************************/
/* background_system()                                              */
/*     return -1 on error, 0 on success                             */
/********************************************************************/

int background_system(char *command)
{
  int res;
  int len;

  if (module_initialized == 0) {
    printf("FATAL: calling 'background_system' but 'start_background_system' was not called\n");
    abort();
  }

  len = strlen(command)+1;
  if (len > MAX_COMMAND) {
    printf("FATAL: command too long. Increase MAX_COMMAND (%d).\n", MAX_COMMAND);
    printf("command was: '%s'\n", command);
    abort();
  }
  /* only one command can run at a time, so let's lock/unlock */
  lock_system();
  write_pipe(command_pipe_write, (char*)&len, sizeof(int));
  write_pipe(command_pipe_write, command, len);
  read_pipe(result_pipe_read, (char*)&res, sizeof(int));
  unlock_system();
  if (res == -1 || !WIFEXITED(res) || WEXITSTATUS(res) != 0) return -1;
  return 0;
}

/********************************************************************/
/* start_background_system()                                        */
/*     initializes the "background system" module                   */
/*     to be called very early by the main processing               */
/********************************************************************/

void start_background_system(void)
{
  int p[2];
  pid_t son;

  module_initialized = 1;

  if (pipe(p) == -1) {
    perror("pipe");
    exit(1);
  }
  command_pipe_read  = p[0];
  command_pipe_write = p[1];

  if (pipe(p) == -1) {
    perror("pipe");
    exit(1);
  }
  result_pipe_read  = p[0];
  result_pipe_write = p[1];

  son = fork();
  if (son == -1) {
    perror("fork");
    exit(1);
  }

  if (son) {
    close(result_pipe_write);
    close(command_pipe_read);
    return;
  }

  close(result_pipe_read);
  close(command_pipe_write);

  background_system_process();
}