[PATCH 2/2] NFSv4/flexfiles: support loosely coupled data servers
From: Jeuk Kim
Date: Wed Jul 08 2026 - 03:48:00 EST
A flexfiles storage device is tightly coupled to the MDS only when the
decoded ds_versions[0].tightly_coupled flag is set (RFC 8435, sections
2.3 and 4.1). The client currently ignores that flag and treats every
data server as tightly coupled, which breaks I/O to loosely coupled DSes.
Two things force that assumption on an NFSv4.1+ DS:
1) nfs4_set_ds_client() always sets NFS_CS_PNFS on the new client, so
EXCHANGE_ID is sent with EXCHGID4_FLAG_USE_PNFS_DS.
2) nfs4_init_ds_session() then calls is_ds_client() and returns -ENODEV
if the reply does not carry EXCHGID4_FLAG_USE_PNFS_DS.
A loosely coupled DS is just a normal NFS server and does not act in the
pNFS DS role, so the client must not require it to advertise that role.
Thread the ds_versions[0].tightly_coupled flag from the flexfiles driver
down to the DS connect path. When it is false, skip both the NFS_CS_PNFS
flag and the is_ds_client() check. The file layout driver always passes
true because NFSv4.1 file layout data servers use the pNFS DS role.
Signed-off-by: Jeuk Kim <jeuk20.kim@xxxxxxxxxxx>
---
fs/nfs/filelayout/filelayoutdev.c | 2 +-
fs/nfs/flexfilelayout/flexfilelayoutdev.c | 3 ++-
fs/nfs/internal.h | 3 ++-
fs/nfs/nfs4client.c | 5 +++--
fs/nfs/nfs4session.c | 5 +++--
fs/nfs/nfs4session.h | 3 ++-
fs/nfs/pnfs.h | 3 ++-
fs/nfs/pnfs_nfs.c | 14 +++++++++-----
8 files changed, 24 insertions(+), 14 deletions(-)
diff --git a/fs/nfs/filelayout/filelayoutdev.c b/fs/nfs/filelayout/filelayoutdev.c
index 7226989ee4d5..d06d303fdcc3 100644
--- a/fs/nfs/filelayout/filelayoutdev.c
+++ b/fs/nfs/filelayout/filelayoutdev.c
@@ -280,7 +280,7 @@ nfs4_fl_prepare_ds(struct pnfs_layout_segment *lseg, u32 ds_idx)
status = nfs4_pnfs_ds_connect(s, ds, devid, dataserver_timeo,
dataserver_retrans, 4,
- s->nfs_client->cl_minorversion);
+ s->nfs_client->cl_minorversion, true);
if (status) {
nfs4_mark_deviceid_unavailable(devid);
ret = NULL;
diff --git a/fs/nfs/flexfilelayout/flexfilelayoutdev.c b/fs/nfs/flexfilelayout/flexfilelayoutdev.c
index 1109462a9699..8be5c730e101 100644
--- a/fs/nfs/flexfilelayout/flexfilelayoutdev.c
+++ b/fs/nfs/flexfilelayout/flexfilelayoutdev.c
@@ -399,7 +399,8 @@ nfs4_ff_layout_prepare_ds(struct pnfs_layout_segment *lseg,
status = nfs4_pnfs_ds_connect(s, ds, &mirror->dss[dss_id].mirror_ds->id_node,
dataserver_timeo, dataserver_retrans,
mirror->dss[dss_id].mirror_ds->ds_versions[0].version,
- mirror->dss[dss_id].mirror_ds->ds_versions[0].minor_version);
+ mirror->dss[dss_id].mirror_ds->ds_versions[0].minor_version,
+ mirror->dss[dss_id].mirror_ds->ds_versions[0].tightly_coupled);
/* connect success, check rsize/wsize limit */
if (!status) {
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index acaeff7ddfdf..030b885d41b9 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -250,7 +250,8 @@ extern struct nfs_client *nfs4_set_ds_client(struct nfs_server *mds_srv,
int ds_addrlen, int ds_proto,
unsigned int ds_timeo,
unsigned int ds_retrans,
- u32 minor_version);
+ u32 minor_version,
+ bool tightly_coupled);
extern struct rpc_clnt *nfs4_find_or_create_ds_client(struct nfs_client *,
struct inode *);
extern void nfs4_session_limit_rwsize(struct nfs_server *server);
diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
index 71c271a1700a..df49efd70641 100644
--- a/fs/nfs/nfs4client.c
+++ b/fs/nfs/nfs4client.c
@@ -791,7 +791,7 @@ static int nfs4_set_client(struct nfs_server *server,
struct nfs_client *nfs4_set_ds_client(struct nfs_server *mds_srv,
const struct sockaddr_storage *ds_addr, int ds_addrlen,
int ds_proto, unsigned int ds_timeo, unsigned int ds_retrans,
- u32 minor_version)
+ u32 minor_version, bool tightly_coupled)
{
struct rpc_timeout ds_timeout;
struct nfs_client *mds_clp = mds_srv->nfs_client;
@@ -838,7 +838,8 @@ struct nfs_client *nfs4_set_ds_client(struct nfs_server *mds_srv,
if (test_bit(NFS_CS_NETUNREACH_FATAL, &mds_clp->cl_flags))
__set_bit(NFS_CS_NETUNREACH_FATAL, &cl_init.init_flags);
- __set_bit(NFS_CS_PNFS, &cl_init.init_flags);
+ if (tightly_coupled)
+ __set_bit(NFS_CS_PNFS, &cl_init.init_flags);
cl_init.max_connect = NFS_MAX_TRANSPORTS;
/*
* Set an authflavor equual to the MDS value. Use the MDS nfs_client
diff --git a/fs/nfs/nfs4session.c b/fs/nfs/nfs4session.c
index 993f0db7cf5e..175390e5b93f 100644
--- a/fs/nfs/nfs4session.c
+++ b/fs/nfs/nfs4session.c
@@ -626,7 +626,8 @@ int nfs4_init_session(struct nfs_client *clp)
return nfs41_check_session_ready(clp);
}
-int nfs4_init_ds_session(struct nfs_client *clp, unsigned long lease_time)
+int nfs4_init_ds_session(struct nfs_client *clp, unsigned long lease_time,
+ bool tightly_coupled)
{
struct nfs4_session *session = clp->cl_session;
int ret;
@@ -652,7 +653,7 @@ int nfs4_init_ds_session(struct nfs_client *clp, unsigned long lease_time)
if (ret)
return ret;
/* Test for the DS role */
- if (!is_ds_client(clp))
+ if (tightly_coupled && !is_ds_client(clp))
return -ENODEV;
return 0;
}
diff --git a/fs/nfs/nfs4session.h b/fs/nfs/nfs4session.h
index d2569f599977..ee2f4baf16a1 100644
--- a/fs/nfs/nfs4session.h
+++ b/fs/nfs/nfs4session.h
@@ -122,7 +122,8 @@ extern int nfs4_setup_session_slot_tables(struct nfs4_session *ses);
extern struct nfs4_session *nfs4_alloc_session(struct nfs_client *clp);
extern void nfs4_destroy_session(struct nfs4_session *session);
extern int nfs4_init_session(struct nfs_client *clp);
-extern int nfs4_init_ds_session(struct nfs_client *, unsigned long);
+extern int nfs4_init_ds_session(struct nfs_client *clp, unsigned long lease_time,
+ bool tightly_coupled);
/*
* Determine if sessions are in use.
diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index eb39859c216c..97ad3366d2b9 100644
--- a/fs/nfs/pnfs.h
+++ b/fs/nfs/pnfs.h
@@ -421,7 +421,8 @@ struct nfs4_pnfs_ds *nfs4_pnfs_ds_add(const struct net *net,
void nfs4_pnfs_v3_ds_connect_unload(void);
int nfs4_pnfs_ds_connect(struct nfs_server *mds_srv, struct nfs4_pnfs_ds *ds,
struct nfs4_deviceid_node *devid, unsigned int timeo,
- unsigned int retrans, u32 version, u32 minor_version);
+ unsigned int retrans, u32 version, u32 minor_version,
+ bool tightly_coupled);
struct nfs4_pnfs_ds_addr *nfs4_decode_mp_ds_addr(struct net *net,
struct xdr_stream *xdr,
gfp_t gfp_flags);
diff --git a/fs/nfs/pnfs_nfs.c b/fs/nfs/pnfs_nfs.c
index 0ff43dbcb7cd..99e54537edcc 100644
--- a/fs/nfs/pnfs_nfs.c
+++ b/fs/nfs/pnfs_nfs.c
@@ -881,7 +881,8 @@ static int _nfs4_pnfs_v4_ds_connect(struct nfs_server *mds_srv,
struct nfs4_pnfs_ds *ds,
unsigned int timeo,
unsigned int retrans,
- u32 minor_version)
+ u32 minor_version,
+ bool tightly_coupled)
{
struct nfs_client *clp = ERR_PTR(-EIO);
struct nfs_client *mds_clp = mds_srv->nfs_client;
@@ -971,12 +972,14 @@ static int _nfs4_pnfs_v4_ds_connect(struct nfs_server *mds_srv,
clp = nfs4_set_ds_client(mds_srv, &da->da_addr,
da->da_addrlen, ds_proto,
- timeo, retrans, minor_version);
+ timeo, retrans, minor_version,
+ tightly_coupled);
if (IS_ERR(clp))
continue;
status = nfs4_init_ds_session(clp,
- mds_srv->nfs_client->cl_lease_time);
+ mds_srv->nfs_client->cl_lease_time,
+ tightly_coupled);
if (status) {
nfs_put_client(clp);
clp = ERR_PTR(-EIO);
@@ -1004,7 +1007,8 @@ static int _nfs4_pnfs_v4_ds_connect(struct nfs_server *mds_srv,
*/
int nfs4_pnfs_ds_connect(struct nfs_server *mds_srv, struct nfs4_pnfs_ds *ds,
struct nfs4_deviceid_node *devid, unsigned int timeo,
- unsigned int retrans, u32 version, u32 minor_version)
+ unsigned int retrans, u32 version, u32 minor_version,
+ bool tightly_coupled)
{
int err;
@@ -1027,7 +1031,7 @@ int nfs4_pnfs_ds_connect(struct nfs_server *mds_srv, struct nfs4_pnfs_ds *ds,
break;
case 4:
err = _nfs4_pnfs_v4_ds_connect(mds_srv, ds, timeo, retrans,
- minor_version);
+ minor_version, tightly_coupled);
break;
default:
dprintk("%s: unsupported DS version %d\n", __func__, version);
--
2.43.0