NFSv4: Add support for application leases underpinned by a delegation

If the NFSv4 client already holds a delegation for a file, then we can
support application leases (i.e. fcntl(fd, F_SETLEASE,...)) because the
underlying delegation guarantees that the file is not being modified on
the server by another client in a way that might conflict with the lease
guarantees.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfs4_fs.h

@@ -323,7 +323,8 @@ extern int update_open_stateid(struct nfs4_state *state,
 				const nfs4_stateid *open_stateid,
 				const nfs4_stateid *deleg_stateid,
 				fmode_t fmode);
-
+extern int nfs4_proc_setlease(struct file *file, long arg,
+			      struct file_lock **lease, void **priv);
 extern int nfs4_proc_get_lease_time(struct nfs_client *clp,
 		struct nfs_fsinfo *fsinfo);
 extern void nfs4_update_changeattr(struct inode *dir,

fs/nfs/nfs4file.c

@@ -435,6 +435,12 @@ void nfs42_ssc_unregister_ops(void)
 }
 #endif /* CONFIG_NFS_V4_2 */
 
+static int nfs4_setlease(struct file *file, long arg, struct file_lock **lease,
+			 void **priv)
+{
+	return nfs4_proc_setlease(file, arg, lease, priv);
+}
+
 const struct file_operations nfs4_file_operations = {
 	.read_iter	= nfs_file_read,
 	.write_iter	= nfs_file_write,
@@ -448,7 +454,7 @@ const struct file_operations nfs4_file_operations = {
 	.splice_read	= generic_file_splice_read,
 	.splice_write	= iter_file_splice_write,
 	.check_flags	= nfs_check_flags,
-	.setlease	= simple_nosetlease,
+	.setlease	= nfs4_setlease,
 #ifdef CONFIG_NFS_V4_2
 	.copy_file_range = nfs4_copy_file_range,
 	.llseek		= nfs4_file_llseek,

fs/nfs/nfs4proc.c

@@ -7438,6 +7438,43 @@ nfs4_proc_lock(struct file *filp, int cmd, struct file_lock *request)
 	return nfs4_retry_setlk(state, cmd, request);
 }
 
+static int nfs4_delete_lease(struct file *file, void **priv)
+{
+	return generic_setlease(file, F_UNLCK, NULL, priv);
+}
+
+static int nfs4_add_lease(struct file *file, long arg, struct file_lock **lease,
+			  void **priv)
+{
+	struct inode *inode = file_inode(file);
+	fmode_t type = arg == F_RDLCK ? FMODE_READ : FMODE_WRITE;
+	int ret;
+
+	/* No delegation, no lease */
+	if (!nfs4_have_delegation(inode, type))
+		return -ENOLCK;
+	ret = generic_setlease(file, arg, lease, priv);
+	if (ret || nfs4_have_delegation(inode, type))
+		return ret;
+	/* We raced with a delegation return */
+	nfs4_delete_lease(file, priv);
+	return -ENOLCK;
+}
+
+int nfs4_proc_setlease(struct file *file, long arg, struct file_lock **lease,
+		       void **priv)
+{
+	switch (arg) {
+	case F_RDLCK:
+	case F_WRLCK:
+		return nfs4_add_lease(file, arg, lease, priv);
+	case F_UNLCK:
+		return nfs4_delete_lease(file, priv);
+	default:
+		return -EINVAL;
+	}
+}
+
 int nfs4_lock_delegation_recall(struct file_lock *fl, struct nfs4_state *state, const nfs4_stateid *stateid)
 {
 	struct nfs_server *server = NFS_SERVER(state->inode);