Make BufFileWrite() void.

It now either returns after it wrote all the data you gave it, or raises
an error.  Not done in back-branches, because it might cause problems
for external code.

Discussion: https://postgr.es/m/CA%2BhUKGJE04G%3D8TLK0DLypT_27D9dR8F1RQgNp0jK6qR0tZGWOw%40mail.gmail.com

src/backend/storage/file/buffile.c

@@ -578,7 +578,7 @@ BufFileRead(BufFile *file, void *ptr, size_t size)
  * Like fwrite() except we assume 1-byte element size and report errors via
  * ereport().
  */
-size_t
+void
 BufFileWrite(BufFile *file, void *ptr, size_t size)
 {
 	size_t		nwritten = 0;
@@ -617,8 +617,6 @@ BufFileWrite(BufFile *file, void *ptr, size_t size)
 		size -= nthistime;
 		nwritten += nthistime;
 	}
-
-	return nwritten;
 }
 
 /*

src/include/storage/buffile.h

@@ -39,7 +39,7 @@ typedef struct BufFile BufFile;
 extern BufFile *BufFileCreateTemp(bool interXact);
 extern void BufFileClose(BufFile *file);
 extern size_t BufFileRead(BufFile *file, void *ptr, size_t size);
-extern size_t BufFileWrite(BufFile *file, void *ptr, size_t size);
+extern void BufFileWrite(BufFile *file, void *ptr, size_t size);
 extern int	BufFileSeek(BufFile *file, int fileno, off_t offset, int whence);
 extern void BufFileTell(BufFile *file, int *fileno, off_t *offset);
 extern int	BufFileSeekBlock(BufFile *file, long blknum);