NFSv4/flexfiles: support loosely coupled data servers

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@samsung.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

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 9ddf0192a0b9..8656ea6af887 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -251,7 +251,8 @@ 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 aff019d2842d..d06bfe317890 100644
--- a/fs/nfs/nfs4client.c
+++ b/fs/nfs/nfs4client.c
@@ -792,7 +792,7 @@ 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;
@@ -839,7 +839,8 @@ 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 673c2b244978..bab81f769636 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 648c95b78eea..b539e1a44d26 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 @@ out:
  */
 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);