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Drupal example source code file (update.inc)

This example Drupal source code file (update.inc) is included in the DevDaily.com "Drupal Source Code Warehouse" project. The intent of this project is to help you "Learn Drupal by Example".

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The update.inc Drupal example source code

<?php
// $Id: update.inc,v 1.87 2011/01/03 18:03:54 webchick Exp $

/**
 * @file
 * Drupal database update API.
 *
 * This file contains functions to perform database updates for a Drupal
 * installation. It is included and used extensively by update.php.
 */

/**
 * Minimum schema version of Drupal 6 required for upgrade to Drupal 7.
 *
 * Upgrades from Drupal 6 to Drupal 7 require that Drupal 6 be running
 * the most recent version, or the upgrade could fail. We can't easily
 * check the Drupal 6 version once the update process has begun, so instead
 * we check the schema version of system.module in the system table.
 */
define('REQUIRED_D6_SCHEMA_VERSION', '6055');

/**
 * Disable any items in the {system} table that are not core compatible.
 */
function update_fix_compatibility() {
  $incompatible = array();
  $result = db_query("SELECT name, type, status FROM {system} WHERE status = 1 AND type IN ('module','theme')");
  foreach ($result as $row) {
    if (update_check_incompatibility($row->name, $row->type)) {
      $incompatible[] = $row->name;
    }
  }
  if (!empty($incompatible)) {
    db_update('system')
      ->fields(array('status' => 0))
      ->condition('name', $incompatible, 'IN')
      ->execute();
  }
}

/**
 * Helper function to test compatibility of a module or theme.
 */
function update_check_incompatibility($name, $type = 'module') {
  static $themes, $modules;

  // Store values of expensive functions for future use.
  if (empty($themes) || empty($modules)) {
    // We need to do a full rebuild here to make sure the database reflects any
    // code changes that were made in the filesystem before the update script
    // was initiated.
    $themes = system_rebuild_theme_data();
    $modules = system_rebuild_module_data();
  }

  if ($type == 'module' && isset($modules[$name])) {
    $file = $modules[$name];
  }
  elseif ($type == 'theme' && isset($themes[$name])) {
    $file = $themes[$name];
  }
  if (!isset($file)
      || !isset($file->info['core'])
      || $file->info['core'] != DRUPAL_CORE_COMPATIBILITY
      || version_compare(phpversion(), $file->info['php']) < 0) {
    return TRUE;
  }
  return FALSE;
}

/**
 * Performs extra steps required to bootstrap when using a Drupal 6 database.
 *
 * Users who still have a Drupal 6 database (and are in the process of
 * updating to Drupal 7) need extra help before a full bootstrap can be
 * achieved. This function does the necessary preliminary work that allows
 * the bootstrap to be successful.
 *
 * No access check has been performed when this function is called, so no
 * irreversible changes to the database are made here.
 */
function update_prepare_d7_bootstrap() {
  // Allow the bootstrap to proceed even if a Drupal 6 settings.php file is
  // still being used.
  include_once DRUPAL_ROOT . '/includes/install.inc';
  drupal_bootstrap(DRUPAL_BOOTSTRAP_CONFIGURATION);
  global $databases, $db_url, $db_prefix, $update_rewrite_settings;
  if (empty($databases) && !empty($db_url)) {
    $databases = update_parse_db_url($db_url, $db_prefix);
    // Record the fact that the settings.php file will need to be rewritten.
    $update_rewrite_settings = TRUE;
    $settings_file = conf_path() . '/settings.php';
    $writable = drupal_verify_install_file($settings_file, FILE_EXIST|FILE_READABLE|FILE_WRITABLE);
    $requirements = array(
      'settings file' => array(
        'title' => 'Settings file',
        'value' => $writable ? 'The settings file is writable.' : 'The settings file is not writable.',
        'severity' => $writable ? REQUIREMENT_OK : REQUIREMENT_ERROR,
        'description' => $writable ? '' : 'Drupal requires write permissions to <em>' . $settings_file . '</em> during the update process. If you are unsure how to grant file permissions, consult the <a href="http://drupal.org/server-permissions">online handbook</a>.',
      ),
    );
    update_extra_requirements($requirements);
  }

  // The new {blocked_ips} table is used in Drupal 7 to store a list of
  // banned IP addresses. If this table doesn't exist then we are still
  // running on a Drupal 6 database, so we suppress the unavoidable errors
  // that occur by creating a static list.
  $GLOBALS['conf']['blocked_ips'] = array();

  // Check that PDO is available and that the correct PDO database driver is
  // loaded. Bootstrapping to DRUPAL_BOOTSTRAP_DATABASE will result in a fatal
  // error otherwise.
  $message = '';
  $pdo_link = 'http://drupal.org/requirements/pdo';
  // Check that PDO is loaded.
  if (!extension_loaded('pdo')) {
    $message = '<h2>PDO is required!</h2><p>Drupal 7 requires PHP ' . DRUPAL_MINIMUM_PHP . ' or higher with the PHP Data Objects (PDO) extension enabled.</p>';
  }
  // The PDO::ATTR_DEFAULT_FETCH_MODE constant is not available in the PECL
  // version of PDO.
  elseif (!defined('PDO::ATTR_DEFAULT_FETCH_MODE')) {
    $message = '<h2>The wrong version of PDO is installed!</h2><p>Drupal 7 requires the PHP Data Objects (PDO) extension from PHP core to be enabled. This system has the older PECL version installed.';
    $pdo_link = 'http://drupal.org/requirements/pdo#pecl';
  }
  // Check that the correct driver is loaded for the database being updated.
  // If we have no driver information (for example, if someone tried to create
  // the Drupal 7 $databases array themselves but did not do it correctly),
  // this message will be confusing, so do not perform the check; instead, just
  // let the database connection fail in the code that follows.
  elseif (isset($databases['default']['default']['driver']) && !in_array($databases['default']['default']['driver'], PDO::getAvailableDrivers())) {
    $message = '<h2>A PDO database driver is required!</h2><p>You need to enable the PDO_' . strtoupper($databases['default']['default']['driver']) . ' database driver for PHP ' . DRUPAL_MINIMUM_PHP . ' or higher so that Drupal 7 can access the database.</p>';
  }
  if ($message) {
    print $message . '<p>See the <a href="' . $pdo_link . '">system requirements page</a> for more information.</p>';
    exit();
  }

  // Allow the database system to work even if the registry has not been
  // created yet.
  drupal_bootstrap(DRUPAL_BOOTSTRAP_DATABASE);

  // If the site has not updated to Drupal 7 yet, check to make sure that it is
  // running an up-to-date version of Drupal 6 before proceeding. Note this has
  // to happen AFTER the database bootstraps because of
  // drupal_get_installed_schema_version().
  $system_schema = drupal_get_installed_schema_version('system');
  if ($system_schema < 7000) {
    $has_required_schema = $system_schema >= REQUIRED_D6_SCHEMA_VERSION;
    $requirements = array(
      'drupal 6 version' => array(
        'title' => 'Drupal 6 version',
        'value' => $has_required_schema ? 'You are running a current version of Drupal 6.' : 'You are not running a current version of Drupal 6',
        'severity' => $has_required_schema ? REQUIREMENT_OK : REQUIREMENT_ERROR,
        'description' => $has_required_schema ? '' : 'Please update your Drupal 6 installation to the most recent version before attempting to upgrade to Drupal 7',
      ),
    );

    // Make sure that the database environment is properly set up.
    try {
      db_run_tasks(db_driver());
    }
    catch (DatabaseTaskException $e) {
      $requirements['database tasks'] = array(
        'title' => 'Database environment',
        'value' => 'There is a problem with your database environment',
        'severity' => REQUIREMENT_ERROR,
        'description' => $e->getMessage(),
      );
    }

    update_extra_requirements($requirements);

    // Allow a D6 session to work, since the upgrade has not been performed yet.
    $d6_session_name = update_get_d6_session_name();
    if (!empty($_COOKIE[$d6_session_name])) {
      // Set the current sid to the one found in the D6 cookie.
      $sid = $_COOKIE[$d6_session_name];
      $_COOKIE[session_name()] = $sid;
      session_id($sid);
    }
  }

  // Create the registry tables.
  if (!db_table_exists('registry')) {
    $schema['registry'] = array(
      'fields' => array(
        'name'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''),
        'type'   => array('type' => 'varchar', 'length' => 9, 'not null' => TRUE, 'default' => ''),
        'filename'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''),
        'module'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''),
        'weight'   => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
      ),
      'primary key' => array('name', 'type'),
      'indexes' => array(
        'hook' => array('type', 'weight', 'module'),
      ),
    );
    db_create_table('registry', $schema['registry']);
  }
  if (!db_table_exists('registry_file')) {
    $schema['registry_file'] = array(
      'fields' => array(
        'filename'   => array('type' => 'varchar', 'length' => 255, 'not null' => TRUE),
        'hash'   => array('type' => 'varchar', 'length' => 64, 'not null' => TRUE),
      ),
      'primary key' => array('filename'),
    );
    db_create_table('registry_file', $schema['registry_file']);
  }

  // Older versions of Drupal 6 do not include the semaphore table, which is
  // required to bootstrap, so we add it now so that we can bootstrap and
  // provide a reasonable error message.
  if (!db_table_exists('semaphore')) {
    $semaphore = array(
      'description' => 'Table for holding semaphores, locks, flags, etc. that cannot be stored as Drupal variables since they must not be cached.',
      'fields' => array(
        'name' => array(
          'description' => 'Primary Key: Unique name.',
          'type' => 'varchar',
          'length' => 255,
          'not null' => TRUE,
          'default' => ''
        ),
        'value' => array(
          'description' => 'A value for the semaphore.',
          'type' => 'varchar',
          'length' => 255,
          'not null' => TRUE,
          'default' => ''
        ),
        'expire' => array(
          'description' => 'A Unix timestamp with microseconds indicating when the semaphore should expire.',
          'type' => 'float',
          'size' => 'big',
          'not null' => TRUE
        ),
      ),
      'indexes' => array(
        'value' => array('value'),
        'expire' => array('expire'),
      ),
      'primary key' => array('name'),
    );
    db_create_table('semaphore', $semaphore);
  }

  // The new cache_bootstrap bin is required to bootstrap to
  // DRUPAL_BOOTSTRAP_SESSION, so create it here rather than in
  // update_fix_d7_requirements().
  if (!db_table_exists('cache_bootstrap')) {
    $cache_bootstrap = array(
      'description' => 'Cache table for data required to bootstrap Drupal, may be routed to a shared memory cache.',
      'fields' => array(
        'cid' => array(
          'description' => 'Primary Key: Unique cache ID.',
          'type' => 'varchar',
          'length' => 255,
          'not null' => TRUE,
          'default' => '',
        ),
        'data' => array(
          'description' => 'A collection of data to cache.',
          'type' => 'blob',
          'not null' => FALSE,
          'size' => 'big',
        ),
        'expire' => array(
          'description' => 'A Unix timestamp indicating when the cache entry should expire, or 0 for never.',
          'type' => 'int',
          'not null' => TRUE,
          'default' => 0,
        ),
        'created' => array(
          'description' => 'A Unix timestamp indicating when the cache entry was created.',
          'type' => 'int',
          'not null' => TRUE,
          'default' => 0,
        ),
        'serialized' => array(
          'description' => 'A flag to indicate whether content is serialized (1) or not (0).',
          'type' => 'int',
          'size' => 'small',
          'not null' => TRUE,
          'default' => 0,
        ),
      ),
      'indexes' => array(
        'expire' => array('expire'),
      ),
      'primary key' => array('cid'),
    );
    db_create_table('cache_bootstrap', $cache_bootstrap);
  }

  // Set a valid timezone for 6 -> 7 upgrade process.
  drupal_bootstrap(DRUPAL_BOOTSTRAP_VARIABLES);
  $timezone_offset = variable_get('date_default_timezone', 0);
  if (is_numeric($timezone_offset)) {
    // Save the original offset.
    variable_set('date_temporary_timezone', $timezone_offset);
    // Set the timezone for this request only.
    $GLOBALS['conf']['date_default_timezone'] = 'UTC';
  }
}

/**
 * A helper function that modules can use to assist with the transformation
 * from numeric block deltas to string block deltas during the 6.x -> 7.x
 * upgrade.
 *
 * @todo This function should be removed in 8.x.
 *
 * @param $sandbox
 *   An array holding data for the batch process.
 * @param $renamed_deltas
 *   An associative array.  Keys are module names, values an associative array
 *   mapping the old block deltas to the new block deltas for the module.
 *   Example:
 *   @code
 *     $renamed_deltas = array(
 *       'mymodule' =>
 *         array(
 *           0 => 'mymodule-block-1',
 *           1 => 'mymodule-block-2',
 *         ),
 *     );
 *   @endcode
 * @param $moved_deltas
 *   An associative array. Keys are source module names, values an associative
 *   array mapping the (possibly renamed) block name to the new module name.
 *   Example:
 *   @code
 *     $moved_deltas = array(
 *       'user' =>
 *         array(
 *           'navigation' => 'system',
 *         ),
 *     );
 *   @endcode
 */
function update_fix_d7_block_deltas(&$sandbox, $renamed_deltas, $moved_deltas) {
  // Loop through each block and make changes to the block tables.
  // Only run this the first time through the batch update.
  if (!isset($sandbox['progress'])) {
    // Determine whether to use the old or new block table names.
    $block_tables = db_table_exists('blocks') ? array('blocks', 'blocks_roles') : array('block', 'block_role');
    foreach ($block_tables as $table) {
      foreach ($renamed_deltas as $module => $deltas) {
        foreach ($deltas as $old_delta => $new_delta) {
          // Only do the update if the old block actually exists.
          $block_exists = db_query("SELECT COUNT(*) FROM {" . $table . "} WHERE module = :module AND delta = :delta", array(
              ':module' => $module,
              ':delta' => $old_delta,
            ))
            ->fetchField();
          if ($block_exists) {
            db_update($table)
              ->fields(array('delta' => $new_delta))
              ->condition('module', $module)
              ->condition('delta', $old_delta)
              ->execute();
          }
        }
      }
      foreach ($moved_deltas as $old_module => $deltas) {
        foreach ($deltas as $delta => $new_module) {
          // Only do the update if the old block actually exists.
          $block_exists = db_query("SELECT COUNT(*) FROM {" . $table . "} WHERE module = :module AND delta = :delta", array(
              ':module' => $old_module,
              ':delta' => $delta,
            ))
            ->fetchField();
          if ($block_exists) {
            db_update($table)
              ->fields(array('module' => $new_module))
              ->condition('module', $old_module)
              ->condition('delta', $delta)
              ->execute();
          }
        }
      }
    }

    // Initialize batch update information.
    $sandbox['progress'] = 0;
    $sandbox['last_user_processed'] = -1;
    $sandbox['max'] = db_query("SELECT COUNT(*) FROM {users} WHERE data IS NOT NULL")->fetchField();
  }
  // Now do the batch update of the user-specific block visibility settings.
  $limit = 100;
  $result = db_select('users', 'u')
    ->fields('u', array('uid', 'data'))
    ->condition('uid', $sandbox['last_user_processed'], '>')
    ->orderBy('uid', 'ASC')
    ->where('data IS NOT NULL')
    ->range(0, $limit)
    ->execute();
  foreach ($result as $row) {
    $data = unserialize($row->data);
    $user_needs_update = FALSE;
    foreach ($renamed_deltas as $module => $deltas) {
      foreach ($deltas as $old_delta => $new_delta) {
        if (isset($data['block'][$module][$old_delta])) {
          // Transfer the old block visibility settings to the newly-renamed
          // block, and mark this user for a database update.
          $data['block'][$module][$new_delta] = $data['block'][$module][$old_delta];
          unset($data['block'][$module][$old_delta]);
          $user_needs_update = TRUE;
        }
      }
    }
    foreach ($moved_deltas as $old_module => $deltas) {
      foreach ($deltas as $delta => $new_module) {
        if (isset($data['block'][$old_module][$delta])) {
          // Transfer the old block visibility settings to the moved
          // block, and mark this user for a database update.
          $data['block'][$new_module][$delta] = $data['block'][$old_module][$delta];
          unset($data['block'][$old_module][$delta]);
          $user_needs_update = TRUE;
        }
      }
    }
    // Update the current user.
    if ($user_needs_update) {
      db_update('users')
        ->fields(array('data' => serialize($data)))
        ->condition('uid', $row->uid)
        ->execute();
    }
    // Update our progress information for the batch update.
    $sandbox['progress']++;
    $sandbox['last_user_processed'] = $row->uid;
  }
  // Indicate our current progress to the batch update system.
  if ($sandbox['progress'] < $sandbox['max']) {
    $sandbox['#finished'] = $sandbox['progress'] / $sandbox['max'];
  }
}

/**
 * Perform Drupal 6.x to 7.x updates that are required for update.php
 * to function properly.
 *
 * This function runs when update.php is run the first time for 7.x,
 * even before updates are selected or performed. It is important
 * that if updates are not ultimately performed that no changes are
 * made which make it impossible to continue using the prior version.
 */
function update_fix_d7_requirements() {
  global $conf;

  // Rewrite the settings.php file if necessary, see
  // update_prepare_d7_bootstrap().
  global $update_rewrite_settings, $db_url, $db_prefix;
  if (!empty($update_rewrite_settings)) {
    $databases = update_parse_db_url($db_url, $db_prefix);
    $salt = drupal_hash_base64(drupal_random_bytes(55));
    file_put_contents(conf_path() . '/settings.php', "\n" . '$databases = ' . var_export($databases, TRUE) . ";\n\$drupal_hash_salt = '$salt';", FILE_APPEND);
  }
  if (drupal_get_installed_schema_version('system') < 7000 && !variable_get('update_d7_requirements', FALSE)) {
    // Change 6.x system table field values to 7.x equivalent.
    // Change field values.
    db_change_field('system', 'schema_version', 'schema_version', array(
     'type' => 'int',
     'size' => 'small',
     'not null' => TRUE,
     'default' => -1)
    );
    db_change_field('system', 'status', 'status', array(
      'type' => 'int', 'not null' => TRUE, 'default' => 0));
    db_change_field('system', 'weight', 'weight', array(
      'type' => 'int', 'not null' => TRUE, 'default' => 0));
    db_change_field('system', 'bootstrap', 'bootstrap', array(
      'type' => 'int', 'not null' => TRUE, 'default' => 0));
    // Drop and recreate 6.x indexes.
    db_drop_index('system', 'bootstrap');
    db_add_index('system', 'bootstrap', array(
      'status', 'bootstrap', array('type', 12), 'weight', 'name'));

    db_drop_index('system' ,'modules');
    db_add_index('system', 'modules', array(array(
      'type', 12), 'status', 'weight', 'name'));

    db_drop_index('system', 'type_name');
    db_add_index('system', 'type_name', array(array('type', 12), 'name'));
    // Add 7.x indexes.
    db_add_index('system', 'system_list', array('weight', 'name'));

    // Add the cache_path table.
    if (db_table_exists('cache_path')) {
      db_drop_table('cache_path');
    }
    require_once('./modules/system/system.install');
    $schema['cache_path'] = system_schema_cache_7054();
    $schema['cache_path']['description'] = 'Cache table used for path alias lookups.';
    db_create_table('cache_path', $schema['cache_path']);

    // system_update_7042() renames columns, but these are needed to bootstrap.
    // Add empty columns for now.
    db_add_field('url_alias', 'source', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));
    db_add_field('url_alias', 'alias', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));

    // Add new columns to {menu_router}.
    db_add_field('menu_router', 'delivery_callback', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));
    db_add_field('menu_router', 'context', array(
      'description' => 'Only for local tasks (tabs) - the context of a local task to control its placement.',
      'type' => 'int',
      'not null' => TRUE,
      'default' => 0,
    ));
    db_drop_index('menu_router', 'tab_parent');
    db_add_index('menu_router', 'tab_parent', array(array('tab_parent', 64), 'weight', 'title'));
    db_add_field('menu_router', 'theme_callback', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));
    db_add_field('menu_router', 'theme_arguments', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => ''));

    // Add the role_permission table.
    $schema['role_permission'] = array(
      'fields' => array(
        'rid' => array(
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
      ),
      'permission' => array(
        'type' => 'varchar',
        'length' => 128,
        'not null' => TRUE,
        'default' => '',
      ),
    ),
    'primary key' => array('rid', 'permission'),
    'indexes' => array(
      'permission' => array('permission'),
      ),
    );
    db_create_table('role_permission', $schema['role_permission']);

    // Drops and recreates semaphore value index.
    db_drop_index('semaphore', 'value');
    db_add_index('semaphore', 'value', array('value'));

    $schema['date_format_type'] = array(
      'description' => 'Stores configured date format types.',
      'fields' => array(
        'type' => array(
          'description' => 'The date format type, e.g. medium.',
          'type' => 'varchar',
          'length' => 64,
          'not null' => TRUE,
        ),
        'title' => array(
          'description' => 'The human readable name of the format type.',
          'type' => 'varchar',
          'length' => 255,
          'not null' => TRUE,
        ),
        'locked' => array(
          'description' => 'Whether or not this is a system provided format.',
          'type' => 'int',
          'size' => 'tiny',
          'default' => 0,
          'not null' => TRUE,
        ),
      ),
      'primary key' => array('type'),
    );

    $schema['date_formats'] = array(
      'description' => 'Stores configured date formats.',
      'fields' => array(
        'dfid' => array(
          'description' => 'The date format identifier.',
          'type' => 'serial',
          'not null' => TRUE,
          'unsigned' => TRUE,
        ),
        'format' => array(
          'description' => 'The date format string.',
          'type' => 'varchar',
          'length' => 100,
          'not null' => TRUE,
        ),
        'type' => array(
          'description' => 'The date format type, e.g. medium.',
          'type' => 'varchar',
          'length' => 64,
          'not null' => TRUE,
        ),
        'locked' => array(
          'description' => 'Whether or not this format can be modified.',
          'type' => 'int',
          'size' => 'tiny',
          'default' => 0,
          'not null' => TRUE,
        ),
      ),
      'primary key' => array('dfid'),
      'unique keys' => array('formats' => array('format', 'type')),
    );

    $schema['date_format_locale'] = array(
      'description' => 'Stores configured date formats for each locale.',
      'fields' => array(
        'format' => array(
          'description' => 'The date format string.',
          'type' => 'varchar',
          'length' => 100,
          'not null' => TRUE,
        ),
        'type' => array(
          'description' => 'The date format type, e.g. medium.',
          'type' => 'varchar',
          'length' => 64,
          'not null' => TRUE,
        ),
        'language' => array(
          'description' => 'A {languages}.language for this format to be used with.',
          'type' => 'varchar',
          'length' => 12,
          'not null' => TRUE,
        ),
      ),
      'primary key' => array('type', 'language'),
    );

    db_create_table('date_format_type', $schema['date_format_type']);
    // Sites that have the Drupal 6 Date module installed already have the
    // following tables.
    if (db_table_exists('date_formats')) {
      db_rename_table('date_formats', 'd6_date_formats');
    }
    db_create_table('date_formats', $schema['date_formats']);
    if (db_table_exists('date_format_locale')) {
      db_rename_table('date_format_locale', 'd6_date_format_locale');
    }
    db_create_table('date_format_locale', $schema['date_format_locale']);

    // Add the queue table.
    $schema['queue'] = array(
      'description' => 'Stores items in queues.',
      'fields' => array(
        'item_id' => array(
          'type' => 'serial',
          'unsigned' => TRUE,
          'not null' => TRUE,
          'description' => 'Primary Key: Unique item ID.',
        ),
        'name' => array(
          'type' => 'varchar',
          'length' => 255,
          'not null' => TRUE,
          'default' => '',
          'description' => 'The queue name.',
        ),
        'data' => array(
          'type' => 'blob',
          'not null' => FALSE,
          'size' => 'big',
          'serialize' => TRUE,
          'description' => 'The arbitrary data for the item.',
        ),
        'expire' => array(
          'type' => 'int',
          'not null' => TRUE,
          'default' => 0,
          'description' => 'Timestamp when the claim lease expires on the item.',
        ),
        'created' => array(
          'type' => 'int',
          'not null' => TRUE,
          'default' => 0,
          'description' => 'Timestamp when the item was created.',
        ),
      ),
      'primary key' => array('item_id'),
      'indexes' => array(
        'name_created' => array('name', 'created'),
        'expire' => array('expire'),
      ),
    );
    // Check for queue table that may remain from D5 or D6, if found
    //drop it.
    if (db_table_exists('queue')) {
      db_drop_table('queue');
    }

    db_create_table('queue', $schema['queue']);

    // Create the sequences table.
    $schema['sequences'] = array(
      'description' => 'Stores IDs.',
      'fields' => array(
        'value' => array(
          'description' => 'The value of the sequence.',
          'type' => 'serial',
          'unsigned' => TRUE,
          'not null' => TRUE,
        ),
       ),
      'primary key' => array('value'),
    );
    // Check for sequences table that may remain from D5 or D6, if found
    //drop it.
    if (db_table_exists('sequences')) {
      db_drop_table('sequences');
    }
    db_create_table('sequences', $schema['sequences']);
    // Initialize the table with the maximum current increment of the tables
    // that will rely on it for their ids.
    $max_aid = db_query('SELECT MAX(aid) FROM {actions_aid}')->fetchField();
    $max_uid = db_query('SELECT MAX(uid) FROM {users}')->fetchField();
    $max_batch_id = db_query('SELECT MAX(bid) FROM {batch}')->fetchField();
    db_insert('sequences')->fields(array('value' => max($max_aid, $max_uid, $max_batch_id)))->execute();

    // Add column for locale context.
    if (db_table_exists('locales_source')) {
      db_add_field('locales_source', 'context', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => '', 'description' => 'The context this string applies to.'));
    }

    // Rename 'site_offline_message' variable to 'maintenance_mode_message'
    // and 'site_offline' variable to 'maintenance_mode'.
    // Old variable is removed in update for system.module, see
    // system_update_7036().
    if ($message = variable_get('site_offline_message', NULL)) {
      variable_set('maintenance_mode_message', $message);
    }
    // Old variable is removed in update for system.module, see
    // system_update_7069().
    $site_offline = variable_get('site_offline', -1);
    if ($site_offline != -1) {
      variable_set('maintenance_mode', $site_offline);
    }

    // Add ssid column and index.
    db_add_field('sessions', 'ssid', array('description' => "Secure session ID. The value is generated by Drupal's session handlers.", 'type' => 'varchar', 'length' => 128, 'not null' => TRUE, 'default' => ''));
    db_add_index('sessions', 'ssid', array('ssid'));
    // Drop existing primary key.
    db_drop_primary_key('sessions');
    // Add new primary key.
    db_add_primary_key('sessions', array('sid', 'ssid'));

    // Allow longer javascript file names.
    if (db_table_exists('languages')) {
      db_change_field('languages', 'javascript', 'javascript', array('type' => 'varchar', 'length' => 64, 'not null' => TRUE, 'default' => ''));
    }

    // Rename action description to label.
    db_change_field('actions', 'description', 'label', array('type' => 'varchar', 'length' => 255, 'not null' => TRUE, 'default' => '0'));

    variable_set('update_d7_requirements', TRUE);
  }

  update_fix_d7_install_profile();
}

/**
 * Register the currently installed profile in the system table.
 *
 * Install profiles are now treated as modules by Drupal, and have an upgrade
 * path based on their schema version in the system table.
 *
 * The install profile will be set to schema_version 0, as it has already been
 * installed. Any other hook_update_N functions provided by the install profile
 * will be run by update.php.
 */
function update_fix_d7_install_profile() {
  $profile = drupal_get_profile();

  $results = db_select('system', 's')
    ->fields('s', array('name', 'schema_version'))
    ->condition('name', $profile)
    ->condition('type', 'module')
    ->execute()
    ->fetchAll();

  if (empty($results)) {
    $filename = 'profiles/' . $profile . '/' . $profile . '.profile';

    // Read profile info file
    $info = drupal_parse_info_file(dirname($filename) . '/' . $profile . '.info');

    // Merge in defaults.
    $info = $info + array(
      'dependencies' => array(),
      'description' => '',
      'package' => 'Other',
      'version' => NULL,
      'php' => DRUPAL_MINIMUM_PHP,
      'files' => array(),
    );

    // The install profile is always required.
    $file->info['required'] = TRUE;

    $values = array(
      'filename' => $filename,
      'name' => $profile,
      'info' => serialize($info),
      'schema_version' => 0,
      'type' => 'module',
      'status' => 1,
      'owner' => '',
    );

    // Install profile hooks are always executed last by the module system
    $values['weight'] = 1000;

    // Initializing the system table entry for the install profile
    db_insert('system')
      ->fields(array_keys($values))
      ->values($values)
      ->execute();

    // Reset the cached schema version.
    drupal_get_installed_schema_version($profile, TRUE);

    // Load the updates again to make sure the install profile updates are loaded
    drupal_load_updates();
  }
}

/**
 * Parse pre-Drupal 7 database connection URLs and return D7 compatible array.
 *
 * @return
 *   Drupal 7 DBTNG compatible array of database connection information.
 */
function update_parse_db_url($db_url, $db_prefix) {
  $databases = array();
  if (!is_array($db_url)) {
    $db_url = array('default' => $db_url);
  }
  foreach ($db_url as $database => $url) {
    $url = parse_url($url);
    $databases[$database]['default'] = array(
      // MySQLi uses the mysql driver.
      'driver' => $url['scheme'] == 'mysqli' ? 'mysql' : $url['scheme'],
      // Remove the leading slash to get the database name.
      'database' => substr(urldecode($url['path']), 1),
      'username' => urldecode($url['user']),
      'password' => isset($url['pass']) ? urldecode($url['pass']) : '',
      'host' => urldecode($url['host']),
      'port' => isset($url['port']) ? urldecode($url['port']) : '',
    );
    if (isset($db_prefix)) {
      $databases[$database]['default']['prefix'] = $db_prefix;
    }
  }
  return $databases;
}

/**
 * Constructs a session name compatible with a D6 environment.
 *
 * @return
 *   D6-compatible session name string.
 *
 * @see drupal_settings_initialize()
 */
function update_get_d6_session_name() {
  global $base_url, $cookie_domain;
  $cookie_secure = ini_get('session.cookie_secure');

  // If a custom cookie domain is set in settings.php, that variable forms
  // the basis of the session name. Re-compute the D7 hashing method to find
  // out if $cookie_domain was used as the session name.
  if (($cookie_secure ? 'SSESS' : 'SESS') . substr(hash('sha256', $cookie_domain), 0, 32) == session_name()) {
    $session_name = $cookie_domain;
  }
  else {
    // Otherwise use $base_url as session name, without the protocol
    // to use the same session identifiers across http and https.
    list( , $session_name) = explode('://', $base_url, 2);
  }

  if ($cookie_secure) {
    $session_name .= 'SSL';
  }

  return 'SESS' . md5($session_name);
}

/**
 * Perform one update and store the results for display on finished page.
 *
 * If an update function completes successfully, it should return a message
 * as a string indicating success, for example:
 * @code
 * return t('New index added successfully.');
 * @endcode
 *
 * Alternatively, it may return nothing. In that case, no message
 * will be displayed at all.
 *
 * If it fails for whatever reason, it should throw an instance of
 * DrupalUpdateException with an appropriate error message, for example:
 * @code
 * throw new DrupalUpdateException(t('Description of what went wrong'));
 * @endcode
 *
 * If an exception is thrown, the current update and all updates that depend on
 * it will be aborted. The schema version will not be updated in this case, and
 * all the aborted updates will continue to appear on update.php as updates
 * that have not yet been run.
 *
 * If an update function needs to be re-run as part of a batch process, it
 * should accept the $sandbox array by reference as its first parameter
 * and set the #finished property to the percentage completed that it is, as a
 * fraction of 1.
 *
 * @param $module
 *   The module whose update will be run.
 * @param $number
 *   The update number to run.
 * @param $dependency_map
 *   An array whose keys are the names of all update functions that will be
 *   performed during this batch process, and whose values are arrays of other
 *   update functions that each one depends on.
 * @param $context
 *   The batch context array.
 *
 * @see update_resolve_dependencies()
 */
function update_do_one($module, $number, $dependency_map, &$context) {
  $function = $module . '_update_' . $number;

  // If this update was aborted in a previous step, or has a dependency that
  // was aborted in a previous step, go no further.
  if (!empty($context['results']['#abort']) && array_intersect($context['results']['#abort'], array_merge($dependency_map, array($function)))) {
    return;
  }

  $ret = array();
  if (function_exists($function)) {
    try {
      $ret['results']['query'] = $function($context['sandbox']);
      $ret['results']['success'] = TRUE;
    }
    // @TODO We may want to do different error handling for different
    // exception types, but for now we'll just log the exception and
    // return the message for printing.
    catch (Exception $e) {
      watchdog_exception('update', $e);

      require_once DRUPAL_ROOT . '/includes/errors.inc';
      $variables = _drupal_decode_exception($e);
      // The exception message is run through check_plain() by _drupal_decode_exception().
      $ret['#abort'] = array('success' => FALSE, 'query' => t('%type: !message in %function (line %line of %file).', $variables));
    }
  }

  if (isset($context['sandbox']['#finished'])) {
    $context['finished'] = $context['sandbox']['#finished'];
    unset($context['sandbox']['#finished']);
  }

  if (!isset($context['results'][$module])) {
    $context['results'][$module] = array();
  }
  if (!isset($context['results'][$module][$number])) {
    $context['results'][$module][$number] = array();
  }
  $context['results'][$module][$number] = array_merge($context['results'][$module][$number], $ret);

  if (!empty($ret['#abort'])) {
    // Record this function in the list of updates that were aborted.
    $context['results']['#abort'][] = $function;
  }

  // Record the schema update if it was completed successfully.
  if ($context['finished'] == 1 && empty($ret['#abort'])) {
    drupal_set_installed_schema_version($module, $number);
  }

  $context['message'] = 'Updating ' . check_plain($module) . ' module';
}

/**
 * @class Exception class used to throw error if a module update fails.
 */
class DrupalUpdateException extends Exception { }

/**
 * Start the database update batch process.
 *
 * @param $start
 *   An array whose keys contain the names of modules to be updated during the
 *   current batch process, and whose values contain the number of the first
 *   requested update for that module. The actual updates that are run (and the
 *   order they are run in) will depend on the results of passing this data
 *   through the update dependency system.
 * @param $redirect
 *   Path to redirect to when the batch has finished processing.
 * @param $url
 *   URL of the batch processing page (should only be used for separate
 *   scripts like update.php).
 * @param $batch
 *   Optional parameters to pass into the batch API.
 * @param $redirect_callback
 *   (optional) Specify a function to be called to redirect to the progressive
 *   processing page.
 *
 * @see update_resolve_dependencies()
 */
function update_batch($start, $redirect = NULL, $url = NULL, $batch = array(), $redirect_callback = 'drupal_goto') {
  // During the update, bring the site offline so that schema changes do not
  // affect visiting users.
  $_SESSION['maintenance_mode'] = variable_get('maintenance_mode', FALSE);
  if ($_SESSION['maintenance_mode'] == FALSE) {
    variable_set('maintenance_mode', TRUE);
  }

  // Resolve any update dependencies to determine the actual updates that will
  // be run and the order they will be run in.
  $updates = update_resolve_dependencies($start);

  // Store the dependencies for each update function in an array which the
  // batch API can pass in to the batch operation each time it is called. (We
  // do not store the entire update dependency array here because it is
  // potentially very large.)
  $dependency_map = array();
  foreach ($updates as $function => $update) {
    $dependency_map[$function] = !empty($update['reverse_paths']) ? array_keys($update['reverse_paths']) : array();
  }

  $operations = array();
  foreach ($updates as $update) {
    if ($update['allowed']) {
      // Set the installed version of each module so updates will start at the
      // correct place. (The updates are already sorted, so we can simply base
      // this on the first one we come across in the above foreach loop.)
      if (isset($start[$update['module']])) {
        drupal_set_installed_schema_version($update['module'], $update['number'] - 1);
        unset($start[$update['module']]);
      }
      // Add this update function to the batch.
      $function = $update['module'] . '_update_' . $update['number'];
      $operations[] = array('update_do_one', array($update['module'], $update['number'], $dependency_map[$function]));
    }
  }
  $batch['operations'] = $operations;
  $batch += array(
    'title' => 'Updating',
    'init_message' => 'Starting updates',
    'error_message' => 'An unrecoverable error has occurred. You can find the error message below. It is advised to copy it to the clipboard for reference.',
    'finished' => 'update_finished',
    'file' => 'includes/update.inc',
  );
  batch_set($batch);
  batch_process($redirect, $url, $redirect_callback);
}

/**
 * Finish the update process and store results for eventual display.
 *
 * After the updates run, all caches are flushed. The update results are
 * stored into the session (for example, to be displayed on the update results
 * page in update.php). Additionally, if the site was off-line, now that the
 * update process is completed, the site is set back online.
 *
 * @param $success
 *   Indicate that the batch API tasks were all completed successfully.
 * @param $results
 *   An array of all the results that were updated in update_do_one().
 * @param $operations
 *   A list of all the operations that had not been completed by the batch API.
 *
 * @see update_batch()
 */
function update_finished($success, $results, $operations) {
  // Clear the caches in case the data has been updated.
  drupal_flush_all_caches();

  $_SESSION['update_results'] = $results;
  $_SESSION['update_success'] = $success;
  $_SESSION['updates_remaining'] = $operations;

  // Now that the update is done, we can put the site back online if it was
  // previously in maintenance mode.
  if (isset($_SESSION['maintenance_mode']) && $_SESSION['maintenance_mode'] == FALSE) {
    variable_set('maintenance_mode', FALSE);
    unset($_SESSION['maintenance_mode']);
  }
}

/**
 * Return a list of all the pending database updates.
 *
 * @return
 *   An associative array keyed by module name which contains all information
 *   about database updates that need to be run, and any updates that are not
 *   going to proceed due to missing requirements. The system module will
 *   always be listed first.
 *
 *   The subarray for each module can contain the following keys:
 *   - start: The starting update that is to be processed. If this does not
 *       exist then do not process any updates for this module as there are
 *       other requirements that need to be resolved.
 *   - warning: Any warnings about why this module can not be updated.
 *   - pending: An array of all the pending updates for the module including
 *       the update number and the description from source code comment for
 *       each update function. This array is keyed by the update number.
 */
function update_get_update_list() {
  // Make sure that the system module is first in the list of updates.
  $ret = array('system' => array());

  $modules = drupal_get_installed_schema_version(NULL, FALSE, TRUE);
  foreach ($modules as $module => $schema_version) {
    // Skip uninstalled and incompatible modules.
    if ($schema_version == SCHEMA_UNINSTALLED || update_check_incompatibility($module)) {
      continue;
    }
    // Otherwise, get the list of updates defined by this module.
    $updates = drupal_get_schema_versions($module);
    if ($updates !== FALSE) {
      // module_invoke returns NULL for nonexisting hooks, so if no updates
      // are removed, it will == 0.
      $last_removed = module_invoke($module, 'update_last_removed');
      if ($schema_version < $last_removed) {
        $ret[$module]['warning'] = '<em>' . $module . '</em> module can not be updated. Its schema version is ' . $schema_version . '. Updates up to and including ' . $last_removed . ' have been removed in this release. In order to update <em>' . $module . '</em> module, you will first <a href="http://drupal.org/upgrade">need to upgrade</a> to the last version in which these updates were available.';
        continue;
      }

      $updates = drupal_map_assoc($updates);
      foreach (array_keys($updates) as $update) {
        if ($update > $schema_version) {
          // The description for an update comes from its Doxygen.
          $func = new ReflectionFunction($module . '_update_' . $update);
          $description = str_replace(array("\n", '*', '/'), '', $func->getDocComment());
          $ret[$module]['pending'][$update] = "$update - $description";
          if (!isset($ret[$module]['start'])) {
            $ret[$module]['start'] = $update;
          }
        }
      }
      if (!isset($ret[$module]['start']) && isset($ret[$module]['pending'])) {
        $ret[$module]['start'] = $schema_version;
      }
    }
  }

  if (empty($ret['system'])) {
    unset($ret['system']);
  }
  return $ret;
}

/**
 * Resolves dependencies in a set of module updates, and orders them correctly.
 *
 * This function receives a list of requested module updates and determines an
 * appropriate order to run them in such that all update dependencies are met.
 * Any updates whose dependencies cannot be met are included in the returned
 * array but have the key 'allowed' set to FALSE; the calling function should
 * take responsibility for ensuring that these updates are ultimately not
 * performed.
 *
 * In addition, the returned array also includes detailed information about the
 * dependency chain for each update, as provided by the depth-first search
 * algorithm in drupal_depth_first_search().
 *
 * @param $starting_updates
 *   An array whose keys contain the names of modules with updates to be run
 *   and whose values contain the number of the first requested update for that
 *   module.
 *
 * @return
 *   An array whose keys are the names of all update functions within the
 *   provided modules that would need to be run in order to fulfill the
 *   request, arranged in the order in which the update functions should be
 *   run. (This includes the provided starting update for each module and all
 *   subsequent updates that are available.) The values are themselves arrays
 *   containing all the keys provided by the drupal_depth_first_search()
 *   algorithm, which encode detailed information about the dependency chain
 *   for this update function (for example: 'paths', 'reverse_paths', 'weight',
 *   and 'component'), as well as the following additional keys:
 *   - 'allowed': A boolean which is TRUE when the update function's
 *     dependencies are met, and FALSE otherwise. Calling functions should
 *     inspect this value before running the update.
 *   - 'missing_dependencies': An array containing the names of any other
 *     update functions that are required by this one but that are unavailable
 *     to be run. This array will be empty when 'allowed' is TRUE.
 *   - 'module': The name of the module that this update function belongs to.
 *   - 'number': The number of this update function within that module.
 *
 * @see drupal_depth_first_search()
 */
function update_resolve_dependencies($starting_updates) {
  // Obtain a dependency graph for the requested update functions.
  $update_functions = update_get_update_function_list($starting_updates);
  $graph = update_build_dependency_graph($update_functions);

  // Perform the depth-first search and sort the results.
  require_once DRUPAL_ROOT . '/includes/graph.inc';
  drupal_depth_first_search($graph);
  uasort($graph, 'drupal_sort_weight');

  foreach ($graph as $function => &$data) {
    $module = $data['module'];
    $number = $data['number'];
    // If the update function is missing and has not yet been performed, mark
    // it and everything that ultimately depends on it as disallowed.
    if (update_is_missing($module, $number, $update_functions) && !update_already_performed($module, $number)) {
      $data['allowed'] = FALSE;
      foreach (array_keys($data['paths']) as $dependent) {
        $graph[$dependent]['allowed'] = FALSE;
        $graph[$dependent]['missing_dependencies'][] = $function;
      }
    }
    elseif (!isset($data['allowed'])) {
      $data['allowed'] = TRUE;
      $data['missing_dependencies'] = array();
    }
    // Now that we have finished processing this function, remove it from the
    // graph if it was not part of the original list. This ensures that we
    // never try to run any updates that were not specifically requested.
    if (!isset($update_functions[$module][$number])) {
      unset($graph[$function]);
    }
  }

  return $graph;
}

/**
 * Returns an organized list of update functions for a set of modules.
 *
 * @param $starting_updates
 *   An array whose keys contain the names of modules and whose values contain
 *   the number of the first requested update for that module.
 *
 * @return
 *   An array containing all the update functions that should be run for each
 *   module, including the provided starting update and all subsequent updates
 *   that are available. The keys of the array contain the module names, and
 *   each value is an ordered array of update functions, keyed by the update
 *   number.
 *
 * @see update_resolve_dependencies()
 */
function update_get_update_function_list($starting_updates) {
  // Go through each module and find all updates that we need (including the
  // first update that was requested and any updates that run after it).
  $update_functions = array();
  foreach ($starting_updates as $module => $version) {
    $update_functions[$module] = array();
    $updates = drupal_get_schema_versions($module);
    if ($updates !== FALSE) {
      $max_version = max($updates);
      if ($version <= $max_version) {
        foreach ($updates as $update) {
          if ($update >= $version) {
            $update_functions[$module][$update] = $module . '_update_' . $update;
          }
        }
      }
    }
  }
  return $update_functions;
}

/**
 * Constructs a graph which encodes the dependencies between module updates.
 *
 * This function returns an associative array which contains a "directed graph"
 * representation of the dependencies between a provided list of update
 * functions, as well as any outside update functions that they directly depend
 * on but that were not in the provided list. The vertices of the graph
 * represent the update functions themselves, and each edge represents a
 * requirement that the first update function needs to run before the second.
 * For example, consider this graph:
 *
 * system_update_7000 ---> system_update_7001 ---> system_update_7002
 *
 * Visually, this indicates that system_update_7000() must run before
 * system_update_7001(), which in turn must run before system_update_7002().
 *
 * The function takes into account standard dependencies within each module, as
 * shown above (i.e., the fact that each module's updates must run in numerical
 * order), but also finds any cross-module dependencies that are defined by
 * modules which implement hook_update_dependencies(), and builds them into the
 * graph as well.
 *
 * @param $update_functions
 *   An organized array of update functions, in the format returned by
 *   update_get_update_function_list().
 *
 * @return
 *   A multidimensional array representing the dependency graph, suitable for
 *   passing in to drupal_depth_first_search(), but with extra information
 *   about each update function also included. Each array key contains the name
 *   of an update function, including all update functions from the provided
 *   list as well as any outside update functions which they directly depend
 *   on. Each value is an associative array containing the following keys:
 *   - 'edges': A representation of any other update functions that immediately
 *     depend on this one. See drupal_depth_first_search() for more details on
 *     the format.
 *   - 'module': The name of the module that this update function belongs to.
 *   - 'number': The number of this update function within that module.
 *
 * @see drupal_depth_first_search()
 * @see update_resolve_dependencies()
 */
function update_build_dependency_graph($update_functions) {
  // Initialize an array that will define a directed graph representing the
  // dependencies between update functions.
  $graph = array();

  // Go through each update function and build an initial list of dependencies.
  foreach ($update_functions as $module => $functions) {
    $previous_function = NULL;
    foreach ($functions as $number => $function) {
      // Add an edge to the directed graph representing the fact that each
      // update function in a given module must run after the update that
      // numerically precedes it.
      if ($previous_function) {
        $graph[$previous_function]['edges'][$function] = TRUE;
      }
      $previous_function = $function;

      // Define the module and update number associated with this function.
      $graph[$function]['module'] = $module;
      $graph[$function]['number'] = $number;
    }
  }

  // Now add any explicit update dependencies declared by modules.
  $update_dependencies = update_retrieve_dependencies();
  foreach ($graph as $function => $data) {
    if (!empty($update_dependencies[$data['module']][$data['number']])) {
      foreach ($update_dependencies[$data['module']][$data['number']] as $module => $number) {
        $dependency = $module . '_update_' . $number;
        $graph[$dependency]['edges'][$function] = TRUE;
        $graph[$dependency]['module'] = $module;
        $graph[$dependency]['number'] = $number;
      }
    }
  }

  return $graph;
}

/**
 * Determines if a module update is missing or unavailable.
 *
 * @param $module
 *   The name of the module.
 * @param $number
 *   The number of the update within that module.
 * @param $update_functions
 *   An organized array of update functions, in the format returned by
 *   update_get_update_function_list(). This should represent all module
 *   updates that are requested to run at the time this function is called.
 *
 * @return
 *   TRUE if the provided module update is not installed or is not in the
 *   provided list of updates to run; FALSE otherwise.
 */
function update_is_missing($module, $number, $update_functions) {
  return !isset($update_functions[$module][$number]) || !function_exists($update_functions[$module][$number]);
}

/**
 * Determines if a module update has already been performed.
 *
 * @param $module
 *   The name of the module.
 * @param $number
 *   The number of the update within that module.
 *
 * @return
 *   TRUE if the database schema indicates that the update has already been
 *   performed; FALSE otherwise.
 */
function update_already_performed($module, $number) {
  return $number <= drupal_get_installed_schema_version($module);
}

/**
 * Invoke hook_update_dependencies() in all installed modules.
 *
 * This function is similar to module_invoke_all(), with the main difference
 * that it does not require that a module be enabled to invoke its hook, only
 * that it be installed. This allows the update system to properly perform
 * updates even on modules that are currently disabled.
 *
 * @return
 *   An array of return values obtained by merging the results of the
 *   hook_update_dependencies() implementations in all installed modules.
 *
 * @see module_invoke_all()
 * @see hook_update_dependencies()
 */
function update_retrieve_dependencies() {
  $return = array();
  // Get a list of installed modules, arranged so that we invoke their hooks in
  // the same order that module_invoke_all() does.
  $modules = db_query("SELECT name FROM {system} WHERE type = 'module' AND schema_version != :schema ORDER BY weight ASC, name ASC", array(':schema' => SCHEMA_UNINSTALLED))->fetchCol();
  foreach ($modules as $module) {
    $function = $module . '_update_dependencies';
    if (function_exists($function)) {
      $result = $function();
      // Each implementation of hook_update_dependencies() returns a
      // multidimensional, associative array containing some keys that
      // represent module names (which are strings) and other keys that
      // represent update function numbers (which are integers). We cannot use
      // array_merge_recursive() to properly merge these results, since it
      // treats strings and integers differently. Therefore, we have to
      // explicitly loop through the expected array structure here and perform
      // the merge manually.
      if (isset($result) && is_array($result)) {
        foreach ($result as $module => $module_data) {
          foreach ($module_data as $update => $update_data) {
            foreach ($update_data as $module_dependency => $update_dependency) {
              // If there are redundant dependencies declared for the same
              // update function (so that it is declared to depend on more than
              // one update from a particular module), record the dependency on
              // the highest numbered update here, since that automatically
              // implies the previous ones. For example, if one module's
              // implementation of hook_update_dependencies() required this
              // ordering:
              //
              // system_update_7001 ---> user_update_7000
              //
              // but another module's implementation of the hook required this
              // one:
              //
              // system_update_7002 ---> user_update_7000
              //
              // we record the second one, since system_update_7001() is always
              // guaranteed to run before system_update_7002() anyway (within
              // an individual module, updates are always run in numerical
              // order).
              if (!isset($return[$module][$update][$module_dependency]) || $update_dependency > $return[$module][$update][$module_dependency]) {
                $return[$module][$update][$module_dependency] = $update_dependency;
              }
            }
          }
        }
      }
    }
  }

  return $return;
}

/**
 * @defgroup update-api-6.x-to-7.x Update versions of API functions
 * @{
 * Functions similar to normal API function but not firing hooks.
 *
 * During update, it is impossible to judge the consequences of firing a hook
 * as it might hit a module not yet updated. So simplified versions of some
 * core APIs are provided.
 */

/**
 * @} End of "defgroup update-api-6.x-to-7.x"
 */

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