nfsd: require an explicit option to enable pNFS

Turns out sending out layouts to any client is a bad idea if they
can't get at the storage device, so require explicit admin action
to enable pNFS.

Signed-off-by: Christoph Hellwig <[e-mail]>
Signed-off-by: J. Bruce Fields <[e-mail]>

fs/nfsd/nfs4layouts.c

···
 {
 	struct super_block *sb = exp->ex_path.mnt->mnt_sb;
 
-	if (exp->ex_flags & NFSEXP_NOPNFS)
+	if (!(exp->ex_flags & NFSEXP_PNFS))
 		return;
 
 	if (sb->s_export_op->get_uuid &&

include/uapi/linux/nfsd/export.h

···
  * exported filesystem.
  */
 #define	NFSEXP_V4ROOT		0x10000
-#define NFSEXP_NOPNFS		0x20000
+#define NFSEXP_PNFS		0x20000
 
 /* All flags that we claim to support.  (Note we don't support NOACL.) */
 #define NFSEXP_ALLFLAGS		0x3FE7F