Add const qualifiers to XLogRegister*() functions

Add const qualifiers to XLogRegisterData() and XLogRegisterBufData().
Several unconstify() calls can be removed.

Reviewed-by: Aleksander Alekseev <aleksander@timescale.com>
Discussion: https://www.postgresql.org/message-id/dd889784-9ce7-436a-b4f1-52e4a5e577bd@eisentraut.org

src/backend/access/brin/brin_pageops.c

@@ -193,7 +193,7 @@ brin_doupdate(Relation idxrel, BlockNumber pagesPerRange,
 			XLogRegisterData((char *) &xlrec, SizeOfBrinSamepageUpdate);
 
 			XLogRegisterBuffer(0, oldbuf, REGBUF_STANDARD);
-			XLogRegisterBufData(0, (char *) unconstify(BrinTuple *, newtup), newsz);
+			XLogRegisterBufData(0, (const char *) newtup, newsz);
 
 			recptr = XLogInsert(RM_BRIN_ID, info);
 
@@ -285,7 +285,7 @@ brin_doupdate(Relation idxrel, BlockNumber pagesPerRange,
 			XLogRegisterData((char *) &xlrec, SizeOfBrinUpdate);
 
 			XLogRegisterBuffer(0, newbuf, REGBUF_STANDARD | (extended ? REGBUF_WILL_INIT : 0));
-			XLogRegisterBufData(0, (char *) unconstify(BrinTuple *, newtup), newsz);
+			XLogRegisterBufData(0, (const char *) newtup, newsz);
 
 			/* revmap page */
 			XLogRegisterBuffer(1, revmapbuf, 0);

src/backend/access/transam/README

@@ -586,13 +586,13 @@ void XLogRegisterBuffer(uint8 block_id, Buffer buf, uint8 flags);
     XLogRegisterBufData() is included in the WAL record even if a full-page
     image is taken.
 
-void XLogRegisterData(char *data, int len);
+void XLogRegisterData(const char *data, int len);
 
     XLogRegisterData is used to include arbitrary data in the WAL record.  If
     XLogRegisterData() is called multiple times, the data are appended, and
     will be made available to the redo routine as one contiguous chunk.
 
-void XLogRegisterBufData(uint8 block_id, char *data, int len);
+void XLogRegisterBufData(uint8 block_id, const char *data, int len);
 
     XLogRegisterBufData is used to include data associated with a particular
     buffer that was registered earlier with XLogRegisterBuffer().  If

src/backend/access/transam/xact.c

@@ -5951,7 +5951,7 @@ XactLogCommitRecord(TimestampTz commit_time,
 	{
 		XLogRegisterData((char *) (&xl_twophase), sizeof(xl_xact_twophase));
 		if (xl_xinfo.xinfo & XACT_XINFO_HAS_GID)
-			XLogRegisterData(unconstify(char *, twophase_gid), strlen(twophase_gid) + 1);
+			XLogRegisterData(twophase_gid, strlen(twophase_gid) + 1);
 	}
 
 	if (xl_xinfo.xinfo & XACT_XINFO_HAS_ORIGIN)
@@ -6097,7 +6097,7 @@ XactLogAbortRecord(TimestampTz abort_time,
 	{
 		XLogRegisterData((char *) (&xl_twophase), sizeof(xl_xact_twophase));
 		if (xl_xinfo.xinfo & XACT_XINFO_HAS_GID)
-			XLogRegisterData(unconstify(char *, twophase_gid), strlen(twophase_gid) + 1);
+			XLogRegisterData(twophase_gid, strlen(twophase_gid) + 1);
 	}
 
 	if (xl_xinfo.xinfo & XACT_XINFO_HAS_ORIGIN)

src/backend/access/transam/xlog.c

@@ -1248,7 +1248,7 @@ CopyXLogRecordToWAL(int write_len, bool isLogSwitch, XLogRecData *rdata,
 	written = 0;
 	while (rdata != NULL)
 	{
-		char	   *rdata_data = rdata->data;
+		const char *rdata_data = rdata->data;
 		int			rdata_len = rdata->len;
 
 		while (rdata_len > freespace)

src/backend/access/transam/xloginsert.c

@@ -72,7 +72,7 @@ typedef struct
 	RelFileLocator rlocator;	/* identifies the relation and block */
 	ForkNumber	forkno;
 	BlockNumber block;
-	Page		page;			/* page content */
+	const char *page;			/* page content */
 	uint32		rdata_len;		/* total length of data in rdata chain */
 	XLogRecData *rdata_head;	/* head of the chain of data registered with
 								 * this block */
@@ -138,7 +138,7 @@ static XLogRecData *XLogRecordAssemble(RmgrId rmid, uint8 info,
 									   XLogRecPtr RedoRecPtr, bool doPageWrites,
 									   XLogRecPtr *fpw_lsn, int *num_fpi,
 									   bool *topxid_included);
-static bool XLogCompressBackupBlock(char *page, uint16 hole_offset,
+static bool XLogCompressBackupBlock(const char *page, uint16 hole_offset,
 									uint16 hole_length, char *dest, uint16 *dlen);
 
 /*
@@ -307,7 +307,7 @@ XLogRegisterBuffer(uint8 block_id, Buffer buffer, uint8 flags)
  */
 void
 XLogRegisterBlock(uint8 block_id, RelFileLocator *rlocator, ForkNumber forknum,
-				  BlockNumber blknum, Page page, uint8 flags)
+				  BlockNumber blknum, const char *page, uint8 flags)
 {
 	registered_buffer *regbuf;
 
@@ -361,7 +361,7 @@ XLogRegisterBlock(uint8 block_id, RelFileLocator *rlocator, ForkNumber forknum,
  * XLogRecGetData().
  */
 void
-XLogRegisterData(char *data, uint32 len)
+XLogRegisterData(const char *data, uint32 len)
 {
 	XLogRecData *rdata;
 
@@ -402,7 +402,7 @@ XLogRegisterData(char *data, uint32 len)
  * limited)
  */
 void
-XLogRegisterBufData(uint8 block_id, char *data, uint32 len)
+XLogRegisterBufData(uint8 block_id, const char *data, uint32 len)
 {
 	registered_buffer *regbuf;
 	XLogRecData *rdata;
@@ -648,7 +648,7 @@ XLogRecordAssemble(RmgrId rmid, uint8 info,
 
 		if (include_image)
 		{
-			Page		page = regbuf->page;
+			const char *page = regbuf->page;
 			uint16		compressed_len = 0;
 
 			/*
@@ -941,23 +941,23 @@ XLogRecordAssemble(RmgrId rmid, uint8 info,
  * the length of compressed block image.
  */
 static bool
-XLogCompressBackupBlock(char *page, uint16 hole_offset, uint16 hole_length,
+XLogCompressBackupBlock(const char *page, uint16 hole_offset, uint16 hole_length,
 						char *dest, uint16 *dlen)
 {
 	int32		orig_len = BLCKSZ - hole_length;
 	int32		len = -1;
 	int32		extra_bytes = 0;
-	char	   *source;
+	const char *source;
 	PGAlignedBlock tmp;
 
 	if (hole_length != 0)
 	{
 		/* must skip the hole */
-		source = tmp.data;
-		memcpy(source, page, hole_offset);
-		memcpy(source + hole_offset,
+		memcpy(tmp.data, page, hole_offset);
+		memcpy(tmp.data + hole_offset,
 			   page + (hole_offset + hole_length),
 			   BLCKSZ - (hole_length + hole_offset));
+		source = tmp.data;
 
 		/*
 		 * Extra data needs to be stored in WAL record for the compressed

src/backend/replication/logical/message.c

@@ -63,8 +63,8 @@ LogLogicalMessage(const char *prefix, const char *message, size_t size,
 
 	XLogBeginInsert();
 	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
-	XLogRegisterData(unconstify(char *, prefix), xlrec.prefix_size);
-	XLogRegisterData(unconstify(char *, message), size);
+	XLogRegisterData(prefix, xlrec.prefix_size);
+	XLogRegisterData(message, size);
 
 	/* allow origin filtering */
 	XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);

src/include/access/xlog_internal.h

@@ -312,7 +312,7 @@ typedef struct xl_end_of_recovery
 typedef struct XLogRecData
 {
 	struct XLogRecData *next;	/* next struct in chain, or NULL */
-	char	   *data;			/* start of rmgr data to include */
+	const char *data;			/* start of rmgr data to include */
 	uint32		len;			/* length of rmgr data to include */
 } XLogRecData;
 

src/include/access/xloginsert.h

@@ -44,12 +44,12 @@ extern void XLogBeginInsert(void);
 extern void XLogSetRecordFlags(uint8 flags);
 extern XLogRecPtr XLogInsert(RmgrId rmid, uint8 info);
 extern void XLogEnsureRecordSpace(int max_block_id, int ndatas);
-extern void XLogRegisterData(char *data, uint32 len);
+extern void XLogRegisterData(const char *data, uint32 len);
 extern void XLogRegisterBuffer(uint8 block_id, Buffer buffer, uint8 flags);
 extern void XLogRegisterBlock(uint8 block_id, RelFileLocator *rlocator,
-							  ForkNumber forknum, BlockNumber blknum, char *page,
+							  ForkNumber forknum, BlockNumber blknum, const char *page,
 							  uint8 flags);
-extern void XLogRegisterBufData(uint8 block_id, char *data, uint32 len);
+extern void XLogRegisterBufData(uint8 block_id, const char *data, uint32 len);
 extern void XLogResetInsertion(void);
 extern bool XLogCheckBufferNeedsBackup(Buffer buffer);
 

src/include/storage/bufpage.h

@@ -384,9 +384,9 @@ PageGetMaxOffsetNumber(Page page)
  * Additional functions for access to page headers.
  */
 static inline XLogRecPtr
-PageGetLSN(Page page)
+PageGetLSN(const char *page)
 {
-	return PageXLogRecPtrGet(((PageHeader) page)->pd_lsn);
+	return PageXLogRecPtrGet(((const PageHeaderData *) page)->pd_lsn);
 }
 static inline void
 PageSetLSN(Page page, XLogRecPtr lsn)