nfsd: filter readdir results in V4ROOT case

As with lookup, we treat every boject as a mountpoint and pretend it
doesn't exist if it isn't exported.

The preexisting code here is confusing, but I haven't yet figured out
how to make it clearer.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/nfs4xdr.c

@@ -2196,11 +2196,14 @@ nfsd4_encode_dirent_fattr(struct nfsd4_readdir *cd,
 	 * we will not follow the cross mount and will fill the attribtutes
 	 * directly from the mountpoint dentry.
 	 */
-	if (d_mountpoint(dentry) && !attributes_need_mount(cd->rd_bmval))
-		ignore_crossmnt = 1;
-	else if (d_mountpoint(dentry)) {
+	if (nfsd_mountpoint(dentry, exp)) {
 		int err;
 
+		if (!(exp->ex_flags & NFSEXP_V4ROOT)
+				&& !attributes_need_mount(cd->rd_bmval)) {
+			ignore_crossmnt = 1;
+			goto out_encode;
+		}
 		/*
 		 * Why the heck aren't we just using nfsd_lookup??
 		 * Different "."/".." handling?  Something else?
@@ -2216,6 +2219,7 @@ nfsd4_encode_dirent_fattr(struct nfsd4_readdir *cd,
 			goto out_put;
 
 	}
+out_encode:
 	nfserr = nfsd4_encode_fattr(NULL, exp, dentry, p, buflen, cd->rd_bmval,
 					cd->rd_rqstp, ignore_crossmnt);
 out_put:

fs/nfsd/vfs.c

@@ -170,7 +170,7 @@ static int nfsd_lookup_parent(struct svc_rqst *rqstp, struct dentry *dparent, st
  * For nfsd purposes, we treat V4ROOT exports as though there was an
  * export at *every* directory.
  */
-static int nfsd_mountpoint(struct dentry *dentry, struct svc_export *exp)
+int nfsd_mountpoint(struct dentry *dentry, struct svc_export *exp)
 {
 	if (d_mountpoint(dentry))
 		return 1;

fs/nfsd/vfs.h

@@ -40,6 +40,7 @@ __be32		 nfsd_lookup_dentry(struct svc_rqst *, struct svc_fh *,
 				struct svc_export **, struct dentry **);
 __be32		nfsd_setattr(struct svc_rqst *, struct svc_fh *,
 				struct iattr *, int, time_t);
+int nfsd_mountpoint(struct dentry *, struct svc_export *);
 #ifdef CONFIG_NFSD_V4
 __be32          nfsd4_set_nfs4_acl(struct svc_rqst *, struct svc_fh *,
                     struct nfs4_acl *);