options: add ->hide_on_set

Normally we hide children if the parent isn't set, but for some
options it's the other way around.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/parse.h b/parse.h
index fe3b6bc..83cb5b1 100644
--- a/parse.h
+++ b/parse.h
@@ -62,6 +62,7 @@
 	struct value_pair posval[PARSE_MAX_VP];/* possible values */
 	const char *parent;		/* parent option */
 	int hide;			/* hide if parent isn't set */
+	int hide_on_set;		/* hide on set, not on unset */
 	const char *inverse;		/* if set, apply opposite action to this option */
 	struct fio_option *inv_opt;	/* cached lookup */
 	int (*verify)(struct fio_option *, void *);