[RFC PATCH] NFS: allow deprecation of NFS UDP protocol

[Olga Kornievskaia <olga.kornievskaia@gmail.com>]

From: Olga Kornievskaia <kolga@netapp.com>

Add a kernel config CONFIG_NFS_DISABLE_UDP_SUPPORT to disallow NFS
UDP mounts.

I took the same approach as Chuck's deprecation of DES enc types
to start with default to still allow but I think the ultimate
goal is to disable

Question: how do we have folks trying this unless we set it to false?

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
---
 fs/nfs/Kconfig  | 10 ++++++++++
 fs/nfs/client.c |  4 ++++
 fs/nfs/super.c  |  8 ++++++++
 3 files changed, 22 insertions(+)

diff --git a/fs/nfs/Kconfig b/fs/nfs/Kconfig
index 295a7a2..6320113 100644
--- a/fs/nfs/Kconfig
+++ b/fs/nfs/Kconfig
@@ -196,3 +196,13 @@ 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 n
+	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.
+	  The default is N because many deployments still use UDP.
diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 02110a3..24ca314 100644
--- a/fs/nfs/client.c
+++ b/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;
+#ifdef 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;
+#ifdef CONFIG_NFS_DISABLE_UDP_SUPPORT
 		case XPRT_TRANSPORT_UDP:
 			nlm_init.protocol = IPPROTO_UDP;
+#endif
 	}
 
 	host = nlmclnt_init(&nlm_init);
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index a84df7d6..21e59da 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -1011,7 +1011,9 @@ static void nfs_set_port(struct sockaddr *sap, int *port,
 static void nfs_validate_transport_protocol(struct nfs_parsed_mount_data *mnt)
 {
 	switch (mnt->nfs_server.protocol) {
+#ifdef CONFIG_NFS_DISABLE_UDP_SUPPORT
 	case XPRT_TRANSPORT_UDP:
+#endif
 	case XPRT_TRANSPORT_TCP:
 	case XPRT_TRANSPORT_RDMA:
 		break;
@@ -1033,8 +1035,10 @@ static void nfs_set_mount_transport_protocol(struct nfs_parsed_mount_data *mnt)
 			return;
 	switch (mnt->nfs_server.protocol) {
 	case XPRT_TRANSPORT_UDP:
+#ifdef CONFIG_NFS_DISABLE_UDP_SUPPORT
 		mnt->mount_server.protocol = XPRT_TRANSPORT_UDP;
 		break;
+#endif
 	case XPRT_TRANSPORT_TCP:
 	case XPRT_TRANSPORT_RDMA:
 		mnt->mount_server.protocol = XPRT_TRANSPORT_TCP;
@@ -2204,6 +2208,10 @@ static int nfs_validate_text_mount_data(void *options,
 #endif /* CONFIG_NFS_V4 */
 	} else {
 		nfs_set_mount_transport_protocol(args);
+#ifdef CONFIG_NFS_DISABLE_UDP_SUPPORT
+		if (args->nfs_server.protocol == XPRT_TRANSPORT_UDP)
+			goto out_invalid_transport_udp;
+#endif
 		if (args->nfs_server.protocol == XPRT_TRANSPORT_RDMA)
 			port = NFS_RDMA_PORT;
 	}
-- 
1.8.3.1