NFSv4.1: allow nfs_fhget to succeed with mounted on fileid

Commit 28331a46d88459788c8fca72dbb0415cd7f514c9 "Ensure we request the
ordinary fileid when doing readdirplus"
changed the meaning of NFS_ATTR_FATTR_FILEID which used to be set when
FATTR4_WORD1_MOUNTED_ON_FILED was requested.

Allow nfs_fhget to succeed with only a mounted on fileid when crossing
a mountpoint or a referral.

Ask for the fileid of the absent file system if mounted_on_fileid is not
supported.

Signed-off-by: Andy Adamson <andros@netapp.com>
cc:stable@kernel.org [2.6.39]
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index b9056cb..2a55347 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -45,6 +45,17 @@
 		fattr->valid |= NFS_ATTR_FATTR_MOUNTPOINT;
 }
 
+static inline int nfs_attr_use_mounted_on_fileid(struct nfs_fattr *fattr)
+{
+	if (((fattr->valid & NFS_ATTR_FATTR_MOUNTED_ON_FILEID) == 0) ||
+	    (((fattr->valid & NFS_ATTR_FATTR_MOUNTPOINT) == 0) &&
+	     ((fattr->valid & NFS_ATTR_FATTR_V4_REFERRAL) == 0)))
+		return 0;
+
+	fattr->fileid = fattr->mounted_on_fileid;
+	return 1;
+}
+
 struct nfs_clone_mount {
 	const struct super_block *sb;
 	const struct dentry *dentry;