9p: explicitly deny setlease attempts

9p is a remote network protocol, and it doesn't support asynchronous
notifications from the server. Ensure that we don't hand out any leases
since we can't guarantee they'll be broken when a file's contents
change.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>

fs/9p/vfs_file.c

@@ -520,6 +520,7 @@ const struct file_operations v9fs_file_operations = {
 	.splice_read = v9fs_file_splice_read,
 	.splice_write = iter_file_splice_write,
 	.fsync = v9fs_file_fsync,
+	.setlease = simple_nosetlease,
 };
 
 const struct file_operations v9fs_file_operations_dotl = {
@@ -534,4 +535,5 @@ const struct file_operations v9fs_file_operations_dotl = {
 	.splice_read = v9fs_file_splice_read,
 	.splice_write = iter_file_splice_write,
 	.fsync = v9fs_file_fsync_dotl,
+	.setlease = simple_nosetlease,
 };