Update image field settings to use Amazon Simple Storage Service as storage.

.install

/**
 * Update image field settings to use Amazon Simple Storage Service as storage.
 */
function MYMODULE_update_7004() {

  // get list of fields
  $fields = field_info_fields();

  foreach ($fields as $field_name => $field) {

    if ($field['type'] == 'image') {

      // Get the field info
      $field_info = field_info_field($field_name);

      foreach ($field_info['bundles'] as $entity_type => $bundles) {

        foreach ($bundles as $bundle) {

          // Load field instance, the parameters in right order are: entity type, field name, bundle name.
          $instance = field_read_instance($entity_type, $field_name, $bundle);

          unset($instance['widget']['settings']['allowed_schemes']);

          // updated allowed schemes
          if (!in_array('s3', $instance['widget']['settings']['allowed_schemes'])) {
            $instance['widget']['settings']['allowed_schemes']['s3'] = 's3';
          }

          // Save or update field instance.
          field_update_instance($instance);
        }
      }

      // Get a reference to the settings
      $settings = &$field_info['settings'];

      $settings['uri_scheme'] = 's3';

      // Save the field
      field_update_field($field_info);
    }
  }
}