src: sort set elements in netlink_get_setelems()

So users can better track their ruleset via git.

Without sorting, the elements can be listed in a different order
every time the set is created, generating unnecessary git changes.

Mergesort is used. Doesn't sort sets with 'flags interval' set on.

Pablo appends to this changelog description:

Currently these interval set elements are dumped in order. We'll likely
get new representations soon that may not guarantee this anymore, so
let's revisit this later in case we need it.

Without this patch, nft list ruleset with a set containing 40000
elements takes on my laptop:

	real    0m2.742s
	user    0m0.112s
	sys     0m0.280s

With this patch:

	real    0m2.846s
	user    0m0.180s
	sys     0m0.284s

Difference is small, so don't get nft more complicated with yet another
getopt() option, enable this by default.

Signed-off-by: Elise Lennion <elise.lennion@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 100 insertions, 0 deletions

diff --git a/src/mergesort.c b/src/mergesort.c
new file mode 100644
index 00000000..a8353203
--- /dev/null
+++ b/src/mergesort.c
@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2017 Elise Lennion <elise.lennion@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <stdint.h>
+#include <expression.h>
+#include <gmputil.h>
+#include <list.h>
+
+static int expr_msort_cmp(const struct expr *e1, const struct expr *e2);
+
+static int concat_expr_msort_cmp(const struct expr *e1, const struct expr *e2)
+{
+	struct list_head *l = (&e2->expressions)->next;
+	const struct expr *i1, *i2;
+	int ret;
+
+	list_for_each_entry(i1, &e1->expressions, list) {
+		i2 = list_entry(l, typeof(struct expr), list);
+
+		ret = expr_msort_cmp(i1, i2);
+		if (ret)
+			return ret;
+
+		l = l->next;
+	}
+
+	return false;
+}
+
+static int expr_msort_cmp(const struct expr *e1, const struct expr *e2)
+{
+	switch (e1->ops->type) {
+	case EXPR_SET_ELEM:
+		return expr_msort_cmp(e1->key, e2->key);
+	case EXPR_VALUE:
+		return mpz_cmp(e1->value, e2->value);
+	case EXPR_CONCAT:
+		return concat_expr_msort_cmp(e1, e2);
+	case EXPR_MAPPING:
+		return expr_msort_cmp(e1->left, e2->left);
+	default:
+		BUG("Unknown expression %s\n", e1->ops->name);
+	}
+}
+
+static void list_splice_sorted(struct list_head *list, struct list_head *head)
+{
+	struct list_head *h = head->next;
+	struct list_head *l = list->next;
+
+	while (l != list) {
+		if (h == head ||
+		    expr_msort_cmp(list_entry(l, typeof(struct expr), list),
+				   list_entry(h, typeof(struct expr), list)) < 0) {
+			l = l->next;
+			list_add_tail(l->prev, h);
+			continue;
+		}
+
+		h = h->next;
+	}
+}
+
+static void list_cut_middle(struct list_head *list, struct list_head *head)
+{
+	struct list_head *s = head->next;
+	struct list_head *e = head->prev;
+
+	while (e != s) {
+		e = e->prev;
+
+		if (e != s)
+			s = s->next;
+	}
+
+	__list_cut_position(list, head, s);
+}
+
+void list_expr_sort(struct list_head *head)
+{
+	struct list_head *list;
+	LIST_HEAD(temp);
+
+	list = &temp;
+
+	if (list_empty(head) || list_is_singular(head))
+		return;
+
+	list_cut_middle(list, head);
+
+	list_expr_sort(head);
+	list_expr_sort(list);
+
+	list_splice_sorted(list, head);
+}