Revert "nfsd4: fix error return when pseudoroot missing"

Commit f39bde24 fixed the error return from PUTROOTFH in the
case where there is no pseudofilesystem.

This is really a case we shouldn't hit on a correctly configured server:
in the absence of a root filehandle, there's no point accepting version
4 NFS rpc calls at all.

But the shared responsibility between kernel and userspace here means
the kernel on its own can't eliminate the possiblity of this happening.
And we have indeed gotten this wrong in distro's, so new client-side
mount code that attempts to negotiate v4 by default first has to work
around this case.

Therefore when commit f39bde24 arrived at roughly the same
time as the new v4-default mount code, which explicitly checked only for
the previous error, the result was previously fine mounts suddenly
failing.

We'll fix both sides for now: revert the error change, and make the
client-side mount workaround more robust.
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/export.c

@@ -1316,19 +1316,11 @@ rqst_exp_parent(struct svc_rqst *rqstp, struct path *path)
 
 static struct svc_export *find_fsidzero_export(struct svc_rqst *rqstp)
 {
-	struct svc_export *exp;
 	u32 fsidv[2];
 
 	mk_fsid(FSID_NUM, fsidv, 0, 0, 0, NULL);
 
-	exp = rqst_exp_find(rqstp, FSID_NUM, fsidv);
-	/*
-	 * We shouldn't have accepting an nfsv4 request at all if we
-	 * don't have a pseudoexport!:
-	 */
-	if (IS_ERR(exp) && PTR_ERR(exp) == -ENOENT)
-		exp = ERR_PTR(-ESERVERFAULT);
-	return exp;
+	return rqst_exp_find(rqstp, FSID_NUM, fsidv);
 }
 
 /*