Remove unnecessary (char *) casts [checksum]

Remove some (char *) casts related to uses of the pg_checksum_page()
function.  These casts are useless, because everything involved
already has the right type.  Moreover, these casts actually silently
discarded a const qualifier.  The declaration of a higher-level
function needs to be adjusted to fix that.

Reviewed-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Discussion: https://www.postgresql.org/message-id/flat/fd1fcedb-3492-4fc8-9e3e-74b97f2db6c7%40eisentraut.org

contrib/pageinspect/rawpage.c

@@ -357,7 +357,7 @@ page_checksum_internal(PG_FUNCTION_ARGS, enum pageinspect_version ext_version)
 	if (PageIsNew(page))
 		PG_RETURN_NULL();
 
-	PG_RETURN_INT16(pg_checksum_page((char *) page, blkno));
+	PG_RETURN_INT16(pg_checksum_page(page, blkno));
 }
 
 Datum

src/backend/storage/page/bufpage.c

@@ -85,7 +85,7 @@ PageInit(Page page, Size pageSize, Size specialSize)
  * to pgstat.
  */
 bool
-PageIsVerifiedExtended(const PageData *page, BlockNumber blkno, int flags)
+PageIsVerifiedExtended(PageData *page, BlockNumber blkno, int flags)
 {
 	const PageHeaderData *p = (const PageHeaderData *) page;
 	size_t	   *pagebytes;
@@ -100,7 +100,7 @@ PageIsVerifiedExtended(const PageData *page, BlockNumber blkno, int flags)
 	{
 		if (DataChecksumsEnabled())
 		{
-			checksum = pg_checksum_page((char *) page, blkno);
+			checksum = pg_checksum_page(page, blkno);
 
 			if (checksum != p->pd_checksum)
 				checksum_failure = true;
@@ -1534,5 +1534,5 @@ PageSetChecksumInplace(Page page, BlockNumber blkno)
 	if (PageIsNew(page) || !DataChecksumsEnabled())
 		return;
 
-	((PageHeader) page)->pd_checksum = pg_checksum_page((char *) page, blkno);
+	((PageHeader) page)->pd_checksum = pg_checksum_page(page, blkno);
 }

src/include/storage/bufpage.h

@@ -489,7 +489,7 @@ StaticAssertDecl(BLCKSZ == ((BLCKSZ / sizeof(size_t)) * sizeof(size_t)),
 				 "BLCKSZ has to be a multiple of sizeof(size_t)");
 
 extern void PageInit(Page page, Size pageSize, Size specialSize);
-extern bool PageIsVerifiedExtended(const PageData *page, BlockNumber blkno, int flags);
+extern bool PageIsVerifiedExtended(PageData *page, BlockNumber blkno, int flags);
 extern OffsetNumber PageAddItemExtended(Page page, Item item, Size size,
 										OffsetNumber offsetNumber, int flags);
 extern Page PageGetTempPage(const PageData *page);