[PATCH 2/2] NFSD: allow client to use write delegation stateid for READ

[Dai Ngo <dai.ngo@oracle.com>]

Allow read using write delegation stateid granted on OPENs with
OPEN4_SHARE_ACCESS_WRITE only, to accommodate clients whose WRITE
implementation may unavoidably do (e.g., due to buffer cache
constraints).

When this condition is detected in nfsd4_encode_read the access
mode FMODE_READ is temporarily added to the file's f_mode and is
removed when the read is done.

Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
---
 fs/nfsd/nfs4proc.c | 15 ++++++++++++++-
 fs/nfsd/nfs4xdr.c  |  8 ++++++++
 fs/nfsd/xdr4.h     |  1 +
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index f6e06c779d09..be43627bbf78 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -973,7 +973,18 @@ 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 &&
+		(read->rd_wd_stid->sc_type != SC_TYPE_DELEG ||
+		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;
@@ -984,6 +995,8 @@ 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,
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index e67420729ecd..3996678bab3f 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -4498,6 +4498,7 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
 	unsigned long maxcount;
 	__be32 wire_data[2];
 	struct file *file;
+	bool wronly = false;
 
 	if (nfserr)
 		return nfserr;
@@ -4515,10 +4516,17 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
 	maxcount = min_t(unsigned long, read->rd_length,
 			 (xdr->buf->buflen - xdr->buf->len));
 
+	if (!(file->f_mode & FMODE_READ) && read->rd_wd_stid) {
+		/* allow READ using write delegation stateid */
+		wronly = true;
+		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 (wronly)
+		file->f_mode &= ~FMODE_READ;
 	if (nfserr) {
 		xdr_truncate_encode(xdr, eof_offset);
 		return nfserr;
diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
index c26ba86dbdfd..2f053beed899 100644
--- a/fs/nfsd/xdr4.h
+++ b/fs/nfsd/xdr4.h
@@ -426,6 +426,7 @@ 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 {
-- 
2.43.5