NFS: allow deprecation of NFS UDP protocol

Add a kernel config CONFIG_NFS_DISABLE_UDP_SUPPORT to disallow NFS
UDP mounts and enable it by default.
Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/Kconfig

@@ -196,3 +196,12 @@ config NFS_DEBUG
 	depends on NFS_FS && SUNRPC_DEBUG
 	select CRC32
 	default y
+
+config NFS_DISABLE_UDP_SUPPORT
+       bool "NFS: Disable NFS UDP protocol support"
+       depends on NFS_FS
+       default y
+       help
+	 Choose Y here to disable the use of NFS over UDP. NFS over UDP
+	 on modern networks (1Gb+) can lead to data corruption caused by
+	 fragmentation during high loads.

fs/nfs/client.c

@@ -474,6 +474,7 @@ void nfs_init_timeout_values(struct rpc_timeout *to, int proto,
 			to->to_maxval = to->to_initval;
 		to->to_exponential = 0;
 		break;
+#ifndef CONFIG_NFS_DISABLE_UDP_SUPPORT
 	case XPRT_TRANSPORT_UDP:
 		if (retrans == NFS_UNSPEC_RETRANS)
 			to->to_retries = NFS_DEF_UDP_RETRANS;
@@ -484,6 +485,7 @@ void nfs_init_timeout_values(struct rpc_timeout *to, int proto,
 		to->to_maxval = NFS_MAX_UDP_TIMEOUT;
 		to->to_exponential = 1;
 		break;
+#endif
 	default:
 		BUG();
 	}
@@ -580,8 +582,10 @@ static int nfs_start_lockd(struct nfs_server *server)
 		default:
 			nlm_init.protocol = IPPROTO_TCP;
 			break;
+#ifndef CONFIG_NFS_DISABLE_UDP_SUPPORT
 		case XPRT_TRANSPORT_UDP:
 			nlm_init.protocol = IPPROTO_UDP;
+#endif
 	}
 
 	host = nlmclnt_init(&nlm_init);

fs/nfs/fs_context.c

@@ -1215,6 +1215,10 @@ static int nfs_fs_context_validate(struct fs_context *fc)
 		}
 	} else {
 		nfs_set_mount_transport_protocol(ctx);
+#ifdef CONFIG_NFS_DISABLE_UDP_SUPPORT
+	       if (ctx->nfs_server.protocol == XPRT_TRANSPORT_UDP)
+		       goto out_invalid_transport_udp;
+#endif
 		if (ctx->nfs_server.protocol == XPRT_TRANSPORT_RDMA)
 			port = NFS_RDMA_PORT;
 	}