pnfs: track multiple layout types in fsinfo structure

Current NFSv4.1/pNFS client assumes that MDS supports only one layout
type. While it's true for most existing servers, nevertheless, this can
be change in the near future.

For now, this patch just plumbs in the ability to track a list of
layouts in the fsinfo structure. The existing behavior of the client
is preserved, by having it just select the first entry in the list.

Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Signed-off-by: Jeff Layton <jlayton@poochiereds.net>
Reviewed-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index 7cc0dee..f11b26e 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -125,6 +125,11 @@
 		| NFS_ATTR_FATTR_V4_SECURITY_LABEL)
 
 /*
+ * Maximal number of supported layout drivers.
+ */
+#define NFS_MAX_LAYOUT_TYPES 8
+
+/*
  * Info on the file system
  */
 struct nfs_fsinfo {
@@ -139,7 +144,7 @@
 	__u64			maxfilesize;
 	struct timespec		time_delta; /* server time granularity */
 	__u32			lease_time; /* in seconds */
-	__u32			layouttype; /* supported pnfs layout driver */
+	__u32			layouttype[NFS_MAX_LAYOUT_TYPES]; /* supported pnfs layout driver */
 	__u32			blksize; /* preferred pnfs io block size */
 	__u32			clone_blksize; /* granularity of a CLONE operation */
 };