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Commit 7ac3efff authored by Sharvil Nanavati's avatar Sharvil Nanavati Committed by Andre Eisenbach
Browse files

Atomically update config files. 

There's a race condition on shutdown between Java and native code.
A stack shutdown is issued from Java and in the meantime the
calling thread calls System.exit(0). If that line is reached before
the native code has had a chance to shut down cleanly, the system
could be stuck in a bad state.

This change uses rename(2) to replace an existing config file
atomically instead of truncating, writing, and then flushing. In
case of a crash or the race condition above, the config file will
still be valid.

There's an implementation gotcha. The config saving code uses ".new"
as a suffix on the original filename to write to a temporary file.
If a file by that name already exists, it will be overwritten.
parent e0a3e23f

system/osi/src/config.c

+42 −3
Original line number Diff line number Diff line 
/******************************************************************************

 *

 *  Copyright (C) 2014 Google, Inc.

 *

 *  Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0

 *

 *  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.

 *

 ******************************************************************************/



#define LOG_TAG "bt_osi_config"



#include <assert.h>
@@ -231,12 +249,21 @@ bool config_save(const config_t *config, const char *filename) { 
  assert(filename != NULL);

  assert(*filename != '\0');



  FILE *fp = fopen(filename, "wt");

  if (!fp) {

    LOG_ERROR("%s unable to write file '%s': %s", __func__, filename, strerror(errno));

  char *temp_filename = osi_calloc(strlen(filename) + 5);

  if (!temp_filename) {

    LOG_ERROR("%s unable to allocate memory for filename.", __func__);

    return false;

  }



  strcpy(temp_filename, filename);

  strcat(temp_filename, ".new");



  FILE *fp = fopen(temp_filename, "wt");

  if (!fp) {

    LOG_ERROR("%s unable to write file '%s': %s", __func__, temp_filename, strerror(errno));

    goto error;

  }



  for (const list_node_t *node = list_begin(config->sections); node != list_end(config->sections); node = list_next(node)) {

    const section_t *section = (const section_t *)list_node(node);

    fprintf(fp, "[%s]\n", section->name);
@@ -253,7 +280,19 @@ bool config_save(const config_t *config, const char *filename) { 


  fflush(fp);

  fclose(fp);



  if (rename(temp_filename, filename) == -1) {

    LOG_ERROR("%s unable to commit file '%s': %s", __func__, filename, strerror(errno));

    goto error;

  }



  osi_free(temp_filename);

  return true;



error:;

  unlink(temp_filename);

  osi_free(temp_filename);

  return false;

}



static char *trim(char *str) {