[PATCH nft 1/2] src: sort set elements in netlink_get_setelems()

[PATCH nft 1/2] src: sort set elements in netlink_get_setelems()

[Elise Lennion]

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.

Signed-off-by: Elise Lennion <elise.lennion@gmail.com>
---
 include/expression.h |   1 +
 src/Makefile.am      |   1 +
 src/mergesort.c      | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/netlink.c        |   4 +++
 4 files changed, 106 insertions(+)
 create mode 100644 src/mergesort.c

diff --git a/include/expression.h b/include/expression.h
index 71e9c43..ec90265 100644
--- a/include/expression.h
+++ b/include/expression.h
@@ -396,6 +396,7 @@ extern struct expr *range_expr_alloc(const struct location *loc,
 
 extern void compound_expr_add(struct expr *compound, struct expr *expr);
 extern void compound_expr_remove(struct expr *compound, struct expr *expr);
+extern void list_expr_sort(struct list_head *head);
 
 extern struct expr *concat_expr_alloc(const struct location *loc);
 
diff --git a/src/Makefile.am b/src/Makefile.am
index 2a69e19..65cb4b4 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -53,6 +53,7 @@ nft_SOURCES =	main.c				\
 		mnl.c				\
 		iface.c				\
 		services.c			\
+		mergesort.c			\
 		scanner.l			\
 		parser_bison.y
 
diff --git a/src/mergesort.c b/src/mergesort.c
new file mode 100644
index 0000000..a835320
--- /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);
+}
diff --git a/src/netlink.c b/src/netlink.c
index 5f478ff..4135f25 100644
--- a/src/netlink.c
+++ b/src/netlink.c
@@ -1666,6 +1666,10 @@ int netlink_get_setelems(struct netlink_ctx *ctx, const struct handle *h,
 	ctx->set = set;
 	set->init = set_expr_alloc(loc);
 	nftnl_set_elem_foreach(nls, list_setelem_cb, ctx);
+
+	if (!(set->flags & NFT_SET_INTERVAL))
+		list_expr_sort(&ctx->set->init->expressions);
+
 	nftnl_set_free(nls);
 	ctx->set = NULL;
 
-- 
2.7.4

Re: [PATCH nft 1/2] src: sort set elements in netlink_get_setelems()

[Pablo Neira Ayuso]

On Fri, Jan 06, 2017 at 07:43:32PM -0200, Elise Lennion wrote:
> 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.

Applied, thanks Elise! I'm appending this to your description BTW:

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.