In bootstrap mode, don't allow the creation of files if they don't already

exist.

In commit's b9d01fe2 and 3908473c, we have added some code where we
allowed the creation of files during mdopen even if they didn't exist
during the bootstrap mode.  The later commit obviates the need for same.

This was harmless code till now but with an upcoming feature where we don't
allow to create FSM for small tables, this will needlessly create FSM
files.

Author: John Naylor
Reviewed-by: Amit Kapila
Discussion: https://www.postgresql.org/message-id/CAJVSVGWvB13PzpbLEecFuGFc5V2fsO736BsdTakPiPAcdMM5tQ@mail.gmail.com
	    https://www.postgresql.org/message-id/CAA4eK1KsET6sotf+rzOTQfb83pzVEzVhbQi1nxGFYVstVWXUGw@mail.gmail.com

src/backend/storage/smgr/md.c

@@ -310,13 +310,7 @@ mdcreate(SMgrRelation reln, ForkNumber forkNum, bool isRedo)
 	{
 		int			save_errno = errno;
 
-		/*
-		 * During bootstrap, there are cases where a system relation will be
-		 * accessed (by internal backend processes) before the bootstrap
-		 * script nominally creates it.  Therefore, allow the file to exist
-		 * already, even if isRedo is not set.  (See also mdopen)
-		 */
-		if (isRedo || IsBootstrapProcessingMode())
+		if (isRedo)
 			fd = PathNameOpenFile(path, O_RDWR | PG_BINARY);
 		if (fd < 0)
 		{
@@ -570,16 +564,6 @@ mdopen(SMgrRelation reln, ForkNumber forknum, int behavior)
 
 	fd = PathNameOpenFile(path, O_RDWR | PG_BINARY);
 
-	if (fd < 0)
-	{
-		/*
-		 * During bootstrap, there are cases where a system relation will be
-		 * accessed (by internal backend processes) before the bootstrap
-		 * script nominally creates it.  Therefore, accept mdopen() as a
-		 * substitute for mdcreate() in bootstrap mode only. (See mdcreate)
-		 */
-		if (IsBootstrapProcessingMode())
-			fd = PathNameOpenFile(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY);
 	if (fd < 0)
 	{
 		if ((behavior & EXTENSION_RETURN_NULL) &&
@@ -592,7 +576,6 @@ mdopen(SMgrRelation reln, ForkNumber forknum, int behavior)
 				(errcode_for_file_access(),
 				 errmsg("could not open file \"%s\": %m", path)));
 	}
-	}
 
 	pfree(path);