From 063c45667ef3ba3c8a23297b07d42edc8653904c Mon Sep 17 00:00:00 2001
From: Matthias van de Meent <boekewurm+postgres@gmail.com>
Date: Wed, 12 Jul 2023 14:08:36 +0200
Subject: [PATCH v5 6/7] Add RM_INVALID, an invalid resource manager

The resource manager has ID = 0, thus requiring some special
handling in other code. Apart from being generally useful, it is
used in future patches to detect the end of wal in lieu of a zero-ed
fixed-size xl_tot_len field.
---
 src/backend/access/transam/xlogreader.c | 13 +++++++++++++
 src/bin/pg_waldump/pg_waldump.c         |  4 ++--
 src/include/access/rmgr.h               |  2 +-
 src/include/access/rmgrlist.h           |  1 +
 src/include/access/xlog_internal.h      |  2 +-
 5 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index bebdf1759a..069289847d 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -670,6 +670,19 @@ restart:
 	else
 	{
 		/* XXX: more validation should be done here */
+
+		/*
+		 * RM_INVALID_ID can be an indication of end-of-WAL, or other signs of
+		 * corruption - that byte should be non-0.
+		 */
+		if (record->xl_rmid == RM_INVALID_ID)
+		{
+			report_invalid_record(state,
+								  "invalid resource manager id %u at %X/%X",
+								  (uint32) record->xl_rmid,
+								  LSN_FORMAT_ARGS(RecPtr));
+			goto err;
+		}
 		if (total_len < SizeOfXLogRecord)
 		{
 			report_invalid_record(state,
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index fb6a5e76b1..83058d3b47 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -99,7 +99,7 @@ print_rmgr_list(void)
 {
 	int			i;
 
-	for (i = 0; i <= RM_MAX_BUILTIN_ID; i++)
+	for (i = RM_INVALID_ID + 1; i <= RM_MAX_BUILTIN_ID; i++)
 	{
 		printf("%s\n", GetRmgrDesc(i)->rm_name);
 	}
@@ -967,7 +967,7 @@ main(int argc, char **argv)
 					else
 					{
 						/* then look for builtin rmgrs */
-						for (rmid = 0; rmid <= RM_MAX_BUILTIN_ID; rmid++)
+						for (rmid = RM_INVALID_ID + 1; rmid <= RM_MAX_BUILTIN_ID; rmid++)
 						{
 							if (pg_strcasecmp(optarg, GetRmgrDesc(rmid)->rm_name) == 0)
 							{
diff --git a/src/include/access/rmgr.h b/src/include/access/rmgr.h
index 3b6a497e1b..7038ba0833 100644
--- a/src/include/access/rmgr.h
+++ b/src/include/access/rmgr.h
@@ -41,7 +41,7 @@ typedef enum RmgrIds
 static inline bool
 RmgrIdIsBuiltin(int rmid)
 {
-	return rmid <= RM_MAX_BUILTIN_ID;
+	return rmid <= RM_MAX_BUILTIN_ID && rmid != RM_INVALID_ID;
 }
 
 static inline bool
diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index 463bcb67c5..b53d731f56 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -25,6 +25,7 @@
  */
 
 /* symbol name, textual name, redo, desc, identify, startup, cleanup, mask, decode */
+PG_RMGR(RM_INVALID_ID, "invalid", NULL, NULL, NULL, NULL, NULL, NULL, NULL)
 PG_RMGR(RM_XLOG_ID, "XLOG", xlog_redo, xlog_desc, xlog_identify, NULL, NULL, NULL, xlog_decode)
 PG_RMGR(RM_XACT_ID, "Transaction", xact_redo, xact_desc, xact_identify, NULL, NULL, NULL, xact_decode)
 PG_RMGR(RM_SMGR_ID, "Storage", smgr_redo, smgr_desc, smgr_identify, NULL, NULL, NULL, NULL)
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 9413836a6a..2277b32d05 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD113	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD114	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
-- 
2.40.1