NFS/pnfs: Separate NFSv3 DS and MDS traffic

If a NFSv3 server is being used as both a DS and as a regular NFSv3 server,
we may want to keep the IO traffic on a separate TCP connection, since
it will typically have very different timeout characteristics.

This patch therefore sets up a flag to separate the two modes of operation
for the nfs_client.

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

fs/nfs/client.c

@@ -312,6 +312,12 @@ again:
 		/* Match nfsv4 minorversion */
 		if (clp->cl_minorversion != data->minorversion)
 			continue;
+
+		/* Match request for a dedicated DS */
+		if (test_bit(NFS_CS_DS, &data->init_flags) !=
+		    test_bit(NFS_CS_DS, &clp->cl_flags))
+			continue;
+
 		/* Match the full socket address */
 		if (!rpc_cmp_addr_port(sap, clap))
 			/* Match all xprt_switch full socket addresses */

fs/nfs/nfs3client.c

@@ -109,6 +109,7 @@ struct nfs_client *nfs3_set_ds_client(struct nfs_server *mds_srv,
 		__set_bit(NFS_CS_NORESVPORT, &cl_init.init_flags);
 
 	__set_bit(NFS_CS_NOPING, &cl_init.init_flags);
+	__set_bit(NFS_CS_DS, &cl_init.init_flags);
 
 	/* Use the MDS nfs_client cl_ipaddr. */
 	nfs_init_timeout_values(&ds_timeout, ds_proto, ds_timeo, ds_retrans);

include/linux/nfs_fs_sb.h

@@ -46,6 +46,7 @@ struct nfs_client {
 #define NFS_CS_NO_RETRANS_TIMEOUT	4	/* - Disable retransmit timeouts */
 #define NFS_CS_TSM_POSSIBLE	5		/* - Maybe state migration */
 #define NFS_CS_NOPING		6		/* - don't ping on connect */
+#define NFS_CS_DS		7		/* - Server is a DS */
 	struct sockaddr_storage	cl_addr;	/* server identifier */
 	size_t			cl_addrlen;
 	char *			cl_hostname;	/* hostname of server */