pnfs: Add layout driver flag PNFS_LAYOUTGET_ON_OPEN

Driver can set flag to allow LAYOUTGET to be sent with OPEN.
Signed-off-by: Fred Isaman <fred.isaman@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/flexfilelayout/flexfilelayout.c

@@ -2347,6 +2347,7 @@ static struct pnfs_layoutdriver_type flexfilelayout_type = {
 	.id			= LAYOUT_FLEX_FILES,
 	.name			= "LAYOUT_FLEX_FILES",
 	.owner			= THIS_MODULE,
+	.flags			= PNFS_LAYOUTGET_ON_OPEN,
 	.set_layoutdriver	= ff_layout_set_layoutdriver,
 	.alloc_layout_hdr	= ff_layout_alloc_layout_hdr,
 	.free_layout_hdr	= ff_layout_free_layout_hdr,

fs/nfs/pnfs.h

@@ -110,6 +110,7 @@ enum layoutdriver_policy_flags {
 	PNFS_LAYOUTRET_ON_SETATTR	= 1 << 0,
 	PNFS_LAYOUTRET_ON_ERROR		= 1 << 1,
 	PNFS_READ_WHOLE_PAGE		= 1 << 2,
+	PNFS_LAYOUTGET_ON_OPEN		= 1 << 3,
 };
 
 struct nfs4_deviceid_node;