[PATCH V4 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).

For write delegation granted for OPEN with OPEN4_SHARE_ACCESS_WRITE
a new nfsd_file and a struct file are allocated to use for reads.
The nfsd_file is freed when the file is closed by release_all_access.

Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
---
 fs/nfsd/nfs4state.c | 44 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 36 insertions(+), 8 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index b533225e57cf..35018af4e7fb 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -6126,6 +6126,34 @@ nfs4_delegation_stat(struct nfs4_delegation *dp, struct svc_fh *currentfh,
 	return rc == 0;
 }
 
+/*
+ * Add NFS4_SHARE_ACCESS_READ to the write delegation granted on OPEN
+ * with NFS4_SHARE_ACCESS_WRITE by allocating separate nfsd_file and
+ * struct file to be used for read with delegation stateid.
+ *
+ */
+static bool
+nfsd4_add_rdaccess_to_wrdeleg(struct svc_rqst *rqstp, struct nfsd4_open *open,
+			      struct svc_fh *fh, struct nfs4_ol_stateid *stp)
+{
+	struct nfs4_file *fp;
+	struct nfsd_file *nf = NULL;
+
+	if ((open->op_share_access & NFS4_SHARE_ACCESS_BOTH) ==
+			NFS4_SHARE_ACCESS_WRITE) {
+		if (nfsd_file_acquire_opened(rqstp, fh, NFSD_MAY_READ, NULL, &nf))
+			return (false);
+		fp = stp->st_stid.sc_file;
+		spin_lock(&fp->fi_lock);
+		__nfs4_file_get_access(fp, NFS4_SHARE_ACCESS_READ);
+		set_access(NFS4_SHARE_ACCESS_READ, stp);
+		fp = stp->st_stid.sc_file;
+		fp->fi_fds[O_RDONLY] = nf;
+		spin_unlock(&fp->fi_lock);
+	}
+	return (true);
+}
+
 /*
  * The Linux NFS server does not offer write delegations to NFSv4.0
  * clients in order to avoid conflicts between write delegations and
@@ -6151,8 +6179,9 @@ nfs4_delegation_stat(struct nfs4_delegation *dp, struct svc_fh *currentfh,
  * open or lock state.
  */
 static void
-nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
-		     struct svc_fh *currentfh)
+nfs4_open_delegation(struct svc_rqst *rqstp, struct nfsd4_open *open,
+		     struct nfs4_ol_stateid *stp, struct svc_fh *currentfh,
+		     struct svc_fh *fh)
 {
 	bool deleg_ts = open->op_deleg_want & OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS;
 	struct nfs4_openowner *oo = openowner(stp->st_stateowner);
@@ -6197,7 +6226,8 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
 	memcpy(&open->op_delegate_stateid, &dp->dl_stid.sc_stateid, sizeof(dp->dl_stid.sc_stateid));
 
 	if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE) {
-		if (!nfs4_delegation_stat(dp, currentfh, &stat)) {
+		if ((!nfsd4_add_rdaccess_to_wrdeleg(rqstp, open, fh, stp)) ||
+				!nfs4_delegation_stat(dp, currentfh, &stat)) {
 			nfs4_put_stid(&dp->dl_stid);
 			destroy_delegation(dp);
 			goto out_no_deleg;
@@ -6353,7 +6383,8 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
 	* Attempt to hand out a delegation. No error return, because the
 	* OPEN succeeds even if we fail.
 	*/
-	nfs4_open_delegation(open, stp, &resp->cstate.current_fh);
+	nfs4_open_delegation(rqstp, open, stp,
+		&resp->cstate.current_fh, current_fh);
 
 	/*
 	 * If there is an existing open stateid, it must be updated and
@@ -7098,10 +7129,6 @@ nfs4_find_file(struct nfs4_stid *s, int flags)
 
 	switch (s->sc_type) {
 	case SC_TYPE_DELEG:
-		spin_lock(&s->sc_file->fi_lock);
-		ret = nfsd_file_get(s->sc_file->fi_deleg_file);
-		spin_unlock(&s->sc_file->fi_lock);
-		break;
 	case SC_TYPE_OPEN:
 	case SC_TYPE_LOCK:
 		if (flags & RD_STATE)
@@ -7277,6 +7304,7 @@ nfs4_preprocess_stateid_op(struct svc_rqst *rqstp,
 		status = find_cpntf_state(nn, stateid, &s);
 	if (status)
 		return status;
+
 	status = nfsd4_stid_check_stateid_generation(stateid, s,
 			nfsd4_has_session(cstate));
 	if (status)
-- 
2.43.5