[PATCH] kNFSd: New routine exp_pseudoroot() to find 'root' filehandle for nfsv4

NFSv4 has a concept of a 'root' filehandle (from which all other can
be found via LOOKUP, so no need for mountd).

This patch defines exp_pseudoroot(), which is used to set the filehandle
for the root of the pseudofs. The root is defined to be the export
point with fsid == 0.

fs/nfsd/export.c

@@ -550,6 +550,23 @@ exp_rootfh(struct svc_client *clp, char *path, struct knfsd_fh *f, int maxsize)
 	return err;
 }
 
+/*
+ * Called when we need the filehandle for the root of the pseudofs,
+ * for a given NFSv4 client.   The root is defined to be the
+ * export point with fsid==0
+ */
+int
+exp_pseudoroot(struct svc_client *clp, struct svc_fh *fhp)
+{
+	struct svc_export *exp;
+
+	exp = exp_get_fsid(clp, 0);
+	if (!exp)
+		return nfserr_perm;
+
+	dget(exp->ex_dentry);
+	return fh_compose(fhp, exp, exp->ex_dentry, NULL);
+}
 
 /*
  * Find a valid client given an inet address. We always move the most

include/linux/nfsd/export.h

@@ -100,6 +100,7 @@ struct svc_export *	exp_parent(struct svc_client *clp, struct vfsmount *mnt,
 				   struct dentry *dentry);
 int			exp_rootfh(struct svc_client *, 
 					char *path, struct knfsd_fh *, int maxsize);
+int			exp_pseudoroot(struct svc_client *, struct svc_fh *fhp);
 int			nfserrno(int errno);
 
 static inline struct svc_export *