NFSv4: Document the recover_lost_locks kernel parameter

Rename the new 'recover_locks' kernel parameter to 'recover_lost_locks'
and change the default to 'false'. Document why in
Documentation/kernel-parameters.txt

Move the 'recover_lost_locks' kernel parameter to fs/nfs/super.c to
make it easy to backport to kernels prior to 3.6.x, which don't have
a separate NFSv4 module.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

Documentation/kernel-parameters.txt

@@ -1847,6 +1847,18 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			will be sent.
 			The default is to send the implementation identification
 			information.
+	
+	nfs.recover_lost_locks =
+			[NFSv4] Attempt to recover locks that were lost due
+			to a lease timeout on the server. Please note that
+			doing this risks data corruption, since there are
+			no guarantees that the file will remain unchanged
+			after the locks are lost.
+			If you want to enable the kernel legacy behaviour of
+			attempting to recover these locks, then set this
+			parameter to '1'.
+			The default parameter value of '0' causes the kernel
+			not to attempt recovery of lost locks.
 
 	nfsd.nfs4_disable_idmapping=
 			[NFSv4] When set to the default of '1', the NFSv4

fs/nfs/nfs4_fs.h

@@ -372,6 +372,7 @@ struct dentry *nfs4_try_mount(int, const char *, struct nfs_mount_info *, struct
 extern bool nfs4_disable_idmapping;
 extern unsigned short max_session_slots;
 extern unsigned short send_implementation_id;
+extern bool recover_lost_locks;
 
 #define NFS4_CLIENT_ID_UNIQ_LEN		(64)
 extern char nfs4_client_id_uniquifier[NFS4_CLIENT_ID_UNIQ_LEN];

fs/nfs/nfs4proc.c

@@ -5523,12 +5523,6 @@ static int nfs4_lock_reclaim(struct nfs4_state *state, struct file_lock *request
 	return err;
 }
 
-bool recover_locks = true;
-module_param(recover_locks, bool, 0644);
-MODULE_PARM_DESC(recover_locks,
-		 "If the server reports that a lock might be lost, "
-		 "try to recovery it risking corruption.");
-
 static int nfs4_lock_expired(struct nfs4_state *state, struct file_lock *request)
 {
 	struct nfs_server *server = NFS_SERVER(state->inode);
@@ -5540,7 +5534,7 @@ static int nfs4_lock_expired(struct nfs4_state *state, struct file_lock *request
 	err = nfs4_set_lock_state(state, request);
 	if (err != 0)
 		return err;
-	if (!recover_locks) {
+	if (!recover_lost_locks) {
 		set_bit(NFS_LOCK_LOST, &request->fl_u.nfs4_fl.owner->ls_flags);
 		return 0;
 	}

fs/nfs/super.c

@@ -2758,6 +2758,7 @@ bool nfs4_disable_idmapping = true;
 unsigned short max_session_slots = NFS4_DEF_SLOT_TABLE_SIZE;
 unsigned short send_implementation_id = 1;
 char nfs4_client_id_uniquifier[NFS4_CLIENT_ID_UNIQ_LEN] = "";
+bool recover_lost_locks = false;
 
 EXPORT_SYMBOL_GPL(nfs_callback_set_tcpport);
 EXPORT_SYMBOL_GPL(nfs_callback_tcpport);
@@ -2766,6 +2767,7 @@ EXPORT_SYMBOL_GPL(nfs4_disable_idmapping);
 EXPORT_SYMBOL_GPL(max_session_slots);
 EXPORT_SYMBOL_GPL(send_implementation_id);
 EXPORT_SYMBOL_GPL(nfs4_client_id_uniquifier);
+EXPORT_SYMBOL_GPL(recover_lost_locks);
 
 #define NFS_CALLBACK_MAXPORTNR (65535U)
 
@@ -2803,4 +2805,10 @@ MODULE_PARM_DESC(send_implementation_id,
 		"Send implementation ID with NFSv4.1 exchange_id");
 MODULE_PARM_DESC(nfs4_unique_id, "nfs_client_id4 uniquifier string");
 
+module_param(recover_lost_locks, bool, 0644);
+MODULE_PARM_DESC(recover_lost_locks,
+		 "If the server reports that a lock might be lost, "
+		 "try to recover it risking data corruption.");
+
+
 #endif /* CONFIG_NFS_V4 */