Mark argument of RegisterCustomRmgr() as const.

doc/src/sgml/custom-rmgr.sgml

@@ -78,7 +78,7 @@ typedef struct RmgrData
  * developers. During development, use RM_EXPERIMENTAL_ID to avoid needlessly
  * reserving a new ID.
  */
-extern void RegisterCustomRmgr(RmgrId rmid, RmgrData *rmgr);
+extern void RegisterCustomRmgr(RmgrId rmid, const RmgrData *rmgr);
 </programlisting>
   <function>RegisterCustomRmgr</function> must be called from the
   extension module's <link linkend="xfunc-c-dynload">_PG_init</link> function.

src/backend/access/transam/rmgr.c

@@ -95,7 +95,7 @@ RmgrNotFound(RmgrId rmid)
  * reserving a new ID.
  */
 void
-RegisterCustomRmgr(RmgrId rmid, RmgrData *rmgr)
+RegisterCustomRmgr(RmgrId rmid, const RmgrData *rmgr)
 {
 	if (rmgr->rm_name == NULL || strlen(rmgr->rm_name) == 0)
 		ereport(ERROR, (errmsg("custom resource manager name is invalid"),

src/include/access/xlog_internal.h

@@ -362,7 +362,7 @@ extern PGDLLIMPORT RmgrData RmgrTable[];
 extern void RmgrStartup(void);
 extern void RmgrCleanup(void);
 extern void RmgrNotFound(RmgrId rmid);
-extern void RegisterCustomRmgr(RmgrId rmid, RmgrData *rmgr);
+extern void RegisterCustomRmgr(RmgrId rmid, const RmgrData *rmgr);
 
 #ifndef FRONTEND
 static inline bool

src/test/modules/test_custom_rmgrs/test_custom_rmgrs.c

@@ -51,7 +51,7 @@ void		testcustomrmgrs_redo(XLogReaderState *record);
 void		testcustomrmgrs_desc(StringInfo buf, XLogReaderState *record);
 const char *testcustomrmgrs_identify(uint8 info);
 
-static RmgrData testcustomrmgrs_rmgr = {
+static const RmgrData testcustomrmgrs_rmgr = {
 	.rm_name = TESTCUSTOMRMGRS_NAME,
 	.rm_redo = testcustomrmgrs_redo,
 	.rm_desc = testcustomrmgrs_desc,