Widen amount-to-flush arguments of FileWriteback and callers.

It's silly to define these counts as narrower than they might someday
need to be.  Also, I believe that the BLCKSZ * nflush calculation in
mdwriteback was capable of overflowing an int.

src/backend/storage/file/fd.c

@@ -1538,28 +1538,28 @@ FilePrefetch(File file, off_t offset, int amount)
 }
 
 void
-FileWriteback(File file, off_t offset, int amount)
+FileWriteback(File file, off_t offset, off_t nbytes)
 {
 	int			returnCode;
 
 	Assert(FileIsValid(file));
 
-	DO_DB(elog(LOG, "FileWriteback: %d (%s) " INT64_FORMAT " %d",
+	DO_DB(elog(LOG, "FileWriteback: %d (%s) " INT64_FORMAT " " INT64_FORMAT,
 			   file, VfdCache[file].fileName,
-			   (int64) offset, amount));
+			   (int64) offset, (int64) nbytes));
 
 	/*
-	 * Caution: do not call pg_flush_data with amount = 0, it could trash the
+	 * Caution: do not call pg_flush_data with nbytes = 0, it could trash the
-	 * file's seek position.
+	 * file's seek position.  We prefer to define that as a no-op here.
 	 */
-	if (amount <= 0)
+	if (nbytes <= 0)
 		return;
 
 	returnCode = FileAccess(file);
 	if (returnCode < 0)
 		return;
 
-	pg_flush_data(VfdCache[file].fd, offset, amount);
+	pg_flush_data(VfdCache[file].fd, offset, nbytes);
 }
 
 int

src/backend/storage/smgr/md.c

@@ -669,15 +669,16 @@ mdprefetch(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum)
  * considerably more efficient than doing so individually.
  */
 void
-mdwriteback(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, int nblocks)
+mdwriteback(SMgrRelation reln, ForkNumber forknum,
+			BlockNumber blocknum, BlockNumber nblocks)
 {
 	/*
 	 * Issue flush requests in as few requests as possible; have to split at
 	 * segment boundaries though, since those are actually separate files.
 	 */
-	while (nblocks != 0)
+	while (nblocks > 0)
 	{
-		int			nflush = nblocks;
+		BlockNumber nflush = nblocks;
 		off_t		seekpos;
 		MdfdVec    *v;
 		int			segnum_start,
@@ -706,7 +707,7 @@ mdwriteback(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, int nbl
 
 		seekpos = (off_t) BLCKSZ *(blocknum % ((BlockNumber) RELSEG_SIZE));
 
-		FileWriteback(v->mdfd_vfd, seekpos, BLCKSZ * nflush);
+		FileWriteback(v->mdfd_vfd, seekpos, (off_t) BLCKSZ * nflush);
 
 		nblocks -= nflush;
 		blocknum += nflush;

src/backend/storage/smgr/smgr.c

@@ -54,7 +54,7 @@ typedef struct f_smgr
 	void		(*smgr_write) (SMgrRelation reln, ForkNumber forknum,
 						 BlockNumber blocknum, char *buffer, bool skipFsync);
 	void		(*smgr_writeback) (SMgrRelation reln, ForkNumber forknum,
-										  BlockNumber blocknum, int nblocks);
+								  BlockNumber blocknum, BlockNumber nblocks);
 	BlockNumber (*smgr_nblocks) (SMgrRelation reln, ForkNumber forknum);
 	void		(*smgr_truncate) (SMgrRelation reln, ForkNumber forknum,
 											  BlockNumber nblocks);
@@ -658,7 +658,7 @@ smgrwrite(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
  */
 void
 smgrwriteback(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
-			  int nblocks)
+			  BlockNumber nblocks)
 {
 	(*(smgrsw[reln->smgr_which].smgr_writeback)) (reln, forknum, blocknum,
 												  nblocks);

src/include/storage/fd.h

@@ -74,7 +74,7 @@ extern int	FileWrite(File file, char *buffer, int amount);
 extern int	FileSync(File file);
 extern off_t FileSeek(File file, off_t offset, int whence);
 extern int	FileTruncate(File file, off_t offset);
-extern void FileWriteback(File file, off_t offset, int amount);
+extern void FileWriteback(File file, off_t offset, off_t nbytes);
 extern char *FilePathName(File file);
 extern int	FileGetRawDesc(File file);
 extern int  FileGetRawFlags(File file);

src/include/storage/smgr.h

@@ -97,7 +97,7 @@ extern void smgrread(SMgrRelation reln, ForkNumber forknum,
 extern void smgrwrite(SMgrRelation reln, ForkNumber forknum,
 		  BlockNumber blocknum, char *buffer, bool skipFsync);
 extern void smgrwriteback(SMgrRelation reln, ForkNumber forknum,
-			  BlockNumber blocknum, int nblocks);
+			  BlockNumber blocknum, BlockNumber nblocks);
 extern BlockNumber smgrnblocks(SMgrRelation reln, ForkNumber forknum);
 extern void smgrtruncate(SMgrRelation reln, ForkNumber forknum,
 			 BlockNumber nblocks);
@@ -125,7 +125,7 @@ extern void mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 extern void mdwrite(SMgrRelation reln, ForkNumber forknum,
 		BlockNumber blocknum, char *buffer, bool skipFsync);
 extern void mdwriteback(SMgrRelation reln, ForkNumber forknum,
-			BlockNumber blocknum, int nblocks);
+			BlockNumber blocknum, BlockNumber nblocks);
 extern BlockNumber mdnblocks(SMgrRelation reln, ForkNumber forknum);
 extern void mdtruncate(SMgrRelation reln, ForkNumber forknum,
 		   BlockNumber nblocks);