[PATCH 19/20] NFS: Add nfs4_unique_id boot parameter

[Chuck Lever <chuck.lever@oracle.com>]

An optional boot parameter is introduced to allow client
administrators to specify a string that the Linux NFS client can
insert into its nfs_client_id4 string, to make it both more globally
unique and more fixed.

If this boot parameter is not specified, the client's nodename is
used, as before.

Client installation procedures can create a unique string (typically,
a UUID) which remains unchanged during the lifetime of that client
instance.  This works just like creating a UUID for the label of the
system's root and boot volumes.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---

 Documentation/filesystems/nfs/nfs.txt |   44 +++++++++++++++++++++++++++++++--
 Documentation/kernel-parameters.txt   |    5 ++++
 fs/nfs/nfs4proc.c                     |   17 +++++++++++++
 3 files changed, 63 insertions(+), 3 deletions(-)

diff --git a/Documentation/filesystems/nfs/nfs.txt b/Documentation/filesystems/nfs/nfs.txt
index f50f26c..f2571c8 100644
--- a/Documentation/filesystems/nfs/nfs.txt
+++ b/Documentation/filesystems/nfs/nfs.txt
@@ -12,9 +12,47 @@ and work is in progress on adding support for minor version 1 of the NFSv4
 protocol.
 
 The purpose of this document is to provide information on some of the
-upcall interfaces that are used in order to provide the NFS client with
-some of the information that it requires in order to fully comply with
-the NFS spec.
+special features of the NFS client that can be configured by system
+administrators.
+
+
+The nfs4_unique_id parameter
+============================
+
+NFSv4 requires clients to identify themselves to servers with a unique
+string.  File open and lock state shared between one client and one server
+is associated with this identity.  To support robust NFSv4 state recovery
+and transparent state migration, this identity string must not change
+across client reboots.
+
+Without any other intervention, the Linux client uses a string that contains
+the local system's node name.  System administrators, however, often do not
+take care to ensure that node names are fully qualified and do not change
+over the lifetime of a client system.  Node names can have other
+administrative requirements that require particular behavior that does not
+work well as part of an nfs_client_id4 string.
+
+The nfs.nfs4_unique_id boot parameter specifies a unique string that can be
+used instead of a system's node name when an NFS client identifies itself to
+a server.  Thus, if the system's node name is not unique, or it changes, its
+nfs.nfs4_unique_id stays the same, preventing collision with other clients
+or loss of state during NFS reboot recovery or transparent state migration.
+
+The nfs.nfs4_unique_id string is typically a UUID, though it can contain
+anything that is believed to be unique across all NFS clients.  An
+nfs4_unique_id string should be chosen when a client system is installed,
+just as a system's root file system gets a fresh UUID in its label at
+install time.
+
+The string should remain fixed for the lifetime of the client.  It can be
+changed safely if care is taken that the client shuts down cleanly and all
+outstanding NFSv4 state has expired, to prevent loss of NFSv4 state.
+
+This string can be stored in an NFS client's grub.conf, or it can be provided
+via a net boot facility such as PXE.  It may also be specified as an nfs.ko
+module parameter.  Specifying a uniquifier string is not support for NFS
+clients running in containers.
+
 
 The DNS resolver
 ================
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index c1601e5..096356b 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1690,6 +1690,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			will be autodetected by the client, and it will fall
 			back to using the idmapper.
 			To turn off this behaviour, set the value to '0'.
+	nfs.nfs4_unique_id=
+			[NFS4] Specify an additional fixed unique ident-
+			ification string that NFSv4 clients can insert into
+			their nfs_client_id4 string.  This is typically a
+			UUID that is generated at system install time.
 
 	nfs.send_implementation_id =
 			[NFSv4.1] Send client implementation identification
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 00b5d02..d112931 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -75,6 +75,12 @@
 
 static unsigned short max_session_slots = NFS4_DEF_SLOT_TABLE_SIZE;
 
+#define NFS4_CLIENT_ID_UNIQ_LEN		(64)
+static char nfs4_client_id_uniquifier[NFS4_CLIENT_ID_UNIQ_LEN] = "";
+module_param_string(nfs4_unique_id, nfs4_client_id_uniquifier,
+			NFS4_CLIENT_ID_UNIQ_LEN, 0600);
+MODULE_PARM_DESC(nfs4_unique_id, "nfs_client_id4 uniquifier string");
+
 struct nfs4_opendata;
 static int _nfs4_proc_open(struct nfs4_opendata *data);
 static int _nfs4_recover_proc_open(struct nfs4_opendata *data);
@@ -3924,16 +3930,27 @@ nfs4_init_nonuniform_client_string(const struct nfs_client *clp,
  *
  * For now I'm going to stick with init_utsname.  We can easily work
  * this out later when the client has container support.
+ *
+ * Specifying a uniquifier string is not supported for NFS clients
+ * running in containers.
  */
 static unsigned int
 nfs4_init_uniform_client_string(const struct nfs_client *clp,
 				char *buf, size_t len)
 {
+	if (nfs4_client_id_uniquifier[0] != '\0')
+		goto have_uniquifier;
 	return scnprintf(buf, len, "Linux NFSv%u.%u %s %s %s uniform",
 				clp->rpc_ops->version, clp->cl_minorversion,
 				init_utsname()->nodename,
 				init_utsname()->domainname,
 				clp->cl_rpcclient->cl_auth->au_ops->au_name);
+
+have_uniquifier:
+	return scnprintf(buf, len, "Linux NFSv%u.%u %s %s uniform",
+				clp->rpc_ops->version, clp->cl_minorversion,
+				nfs4_client_id_uniquifier,
+				clp->cl_rpcclient->cl_auth->au_ops->au_name);
 }
 
 /**