[PATCH v6 4/5] NFSD: allow client to use write delegation stateid for READ

@@ -942,8 +942,18 @@ nfsd4_read(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	/* check stateid */
 	status = nfs4_preprocess_stateid_op(rqstp, cstate, &cstate->current_fh,
 					&read->rd_stateid, RD_STATE,
-					&read->rd_nf, NULL);
-
+					&read->rd_nf, &read->rd_wd_stid);
+	/*
+	 * rd_wd_stid is needed for nfsd4_encode_read to allow write
+	 * delegation stateid used for read. Its refcount is decremented
+	 * by nfsd4_read_release when read is done.
+	 */
+	if (!status && (read->rd_wd_stid->sc_type != NFS4_DELEG_STID ||
+			delegstateid(read->rd_wd_stid)->dl_type !=
+			NFS4_OPEN_DELEGATE_WRITE)) {
+		nfs4_put_stid(read->rd_wd_stid);
+		read->rd_wd_stid = NULL;
+	}
 	read->rd_rqstp = rqstp;
 	read->rd_fhp = &cstate->current_fh;
 	return status;

@@ -953,6 +963,8 @@ nfsd4_read(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 static void
 nfsd4_read_release(union nfsd4_op_u *u)
 {
+	if (u->read.rd_wd_stid)
+		nfs4_put_stid(u->read.rd_wd_stid);
 	if (u->read.rd_nf)
 		nfsd_file_put(u->read.rd_nf);
 	trace_nfsd_read_done(u->read.rd_rqstp, u->read.rd_fhp,

@@ -4125,6 +4125,7 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
 	struct file *file;
 	int starting_len = xdr->buf->len;
 	__be32 *p;
+	fmode_t o_fmode = 0;
 
 	if (nfserr)
 		return nfserr;

@@ -4144,10 +4145,18 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
 	maxcount = min_t(unsigned long, read->rd_length,
 			 (xdr->buf->buflen - xdr->buf->len));
 
+	if (read->rd_wd_stid) {
+		/* allow READ using write delegation stateid */
+		o_fmode = file->f_mode;
+		file->f_mode |= FMODE_READ;
+	}
 	if (file->f_op->splice_read && splice_ok)
 		nfserr = nfsd4_encode_splice_read(resp, read, file, maxcount);
 	else
 		nfserr = nfsd4_encode_readv(resp, read, file, maxcount);
+	if (o_fmode)
+		file->f_mode = o_fmode;
+
 	if (nfserr) {
 		xdr_truncate_encode(xdr, starting_len);
 		return nfserr;

@@ -307,6 +307,8 @@ struct nfsd4_read {
 	struct svc_rqst		*rd_rqstp;          /* response */
 	struct svc_fh		*rd_fhp;            /* response */
 	u32			rd_eof;             /* response */
+
+	struct nfs4_stid	*rd_wd_stid;		/* internal */
 };
 
 struct nfsd4_readdir {