Document validate_fn_t as it stands.

 **/

#define PLURAL(tok) { #tok, #tok "s", 0, 0 }

/** Type of a callback to validate whether a given configuration is

 * well-formed and consistent. See options_trial_assign() for documentation

 * of arguments. */

typedef int (*validate_fn_t)(void*,void*,void*,int,char**);

/**

 * Type of a callback to validate whether a given configuration is

 * well-formed and consistent.

 *

 * The configuration to validate is passed as <b>newval</b>. The previous

 * configuration, if any, is provided in <b>oldval</b>.  The

 * <b>default_val</b> argument receives a configuration object initialized

 * with default values for all its fields.  The <b>from_setconf</b> argument

 * is true iff the input comes from a SETCONF controller command.

 *

 * On success, return 0.  On failure, set *<b>msg_out</b> to a newly allocated

 * error message, and return -1.

 *

 * REFACTORING NOTE: Currently, this callback type is only used from inside

 * config_dump(); later in our refactoring, it will be cleaned up and used

 * more generally.

 */

typedef int (*validate_fn_t)(void *oldval,

                             void *newval,

                             void *default_val,

                             int from_setconf,

                             char **msg_out);

struct config_mgr_t;