config validation: make the "old_options" argument const.

We can't do this with the "options" argument yet, since several
places in the code change those right now.

src/app/config/config.c

@@ -843,7 +843,7 @@ static int parse_outbound_addresses(or_options_t *options, int validate_only,
                                     char **msg);
 static void config_maybe_load_geoip_files_(const or_options_t *options,
                                            const or_options_t *old_options);
-static int options_validate_cb(void *old_options, void *options,
+static int options_validate_cb(const void *old_options, void *options,
                                char **msg);
 static void cleanup_protocol_warning_severity_level(void);
 static void set_protocol_warning_severity_level(int warning_severity);
@@ -1227,7 +1227,8 @@ add_default_fallback_dir_servers,(void))
  * user if we changed any dangerous ones.
  */
 static int
-validate_dir_servers(or_options_t *options, or_options_t *old_options)
+validate_dir_servers(const or_options_t *options,
+                     const or_options_t *old_options)
 {
   config_line_t *cl;
 
@@ -3230,7 +3231,7 @@ compute_publishserverdescriptor(or_options_t *options)
 #define RECOMMENDED_MIN_CIRCUIT_BUILD_TIMEOUT (10)
 
 static int
-options_validate_cb(void *old_options, void *options, char **msg)
+options_validate_cb(const void *old_options, void *options, char **msg)
 {
   in_option_validation = 1;
   int rv = options_validate(old_options, options, msg);
@@ -3430,7 +3431,7 @@ options_validate_single_onion(or_options_t *options, char **msg)
  * On error, tor_strdup an error explanation into *<b>msg</b>.
  */
 STATIC int
-options_validate(or_options_t *old_options, or_options_t *options,
+options_validate(const or_options_t *old_options, or_options_t *options,
                  char **msg)
 {
   config_line_t *cl;

src/app/config/config.h

@@ -277,7 +277,7 @@ STATIC void port_cfg_free_(port_cfg_t *port);
 STATIC void or_options_free_(or_options_t *options);
 STATIC int options_validate_single_onion(or_options_t *options,
                                          char **msg);
-STATIC int options_validate(or_options_t *old_options,
+STATIC int options_validate(const or_options_t *old_options,
                             or_options_t *options,
                             char **msg);
 STATIC int parse_transport_line(const or_options_t *options,

src/app/config/statefile.c

@@ -141,7 +141,7 @@ static const config_var_t state_vars_[] = {
 
 static int or_state_validate(or_state_t *state, char **msg);
 
-static int or_state_validate_cb(void *old_options,
+static int or_state_validate_cb(const void *old_options,
                                 void *options, char **msg);
 
 /** Magic value for or_state_t. */
@@ -268,7 +268,7 @@ validate_transports_in_state(or_state_t *state)
 }
 
 static int
-or_state_validate_cb(void *old_state, void *state, char **msg)
+or_state_validate_cb(const void *old_state, void *state, char **msg)
 {
   /* We don't use these; only options do. Still, we need to match that
    * signature. */

src/feature/dirauth/shared_random_state.c

@@ -60,7 +60,7 @@ DUMMY_TYPECHECK_INSTANCE(sr_disk_state_t);
 #define SR_DISK_STATE_MAGIC 0x98AB1254
 
 static int
-disk_state_validate_cb(void *old_state, void *state, char **msg);
+disk_state_validate_cb(const void *old_state, void *state, char **msg);
 
 /** Array of variables that are saved to disk as a persistent state. */
 static const config_var_t state_vars[] = {
@@ -344,7 +344,7 @@ disk_state_validate(const sr_disk_state_t *state)
 
 /** Validate the disk state (NOP for now). */
 static int
-disk_state_validate_cb(void *old_state, void *state, char **msg)
+disk_state_validate_cb(const void *old_state, void *state, char **msg)
 {
   /* We don't use these; only options do. */
   (void) old_state;

src/lib/confmgt/confparse.h

@@ -68,7 +68,7 @@ typedef struct config_deprecation_t {
  * config_dump(); later in our refactoring, it will be cleaned up and used
  * more generally.
  */
-typedef int (*validate_fn_t)(void *oldval,
+typedef int (*validate_fn_t)(const void *oldval,
                              void *newval,
                              char **msg_out);
 

src/test/test_confparse.c

@@ -103,7 +103,7 @@ static config_deprecation_t test_deprecation_notes[] = {
 };
 
 static int
-test_validate_cb(void *old_options, void *options, char **msg)
+test_validate_cb(const void *old_options, void *options, char **msg)
 {
   (void)old_options;
   (void)msg;