netfilter: nf_tables: Simplify set backend selection

Drop nft_set_type's ability to act as a container of multiple backend
implementations it chooses from. Instead consolidate the whole selection
logic in nft_select_set_ops() and the actual backend provided estimate()
callback.

This turns nf_tables_set_types into a list containing all available
backends which is traversed when selecting one matching userspace
requested criteria.

Also, this change allows to embed nft_set_ops structure into
nft_set_type and pull flags field into the latter as it's only used
during selection phase.

A crucial part of this change is to make sure the new layout respects
hash backend constraints formerly enforced by nft_hash_select_ops()
function: This is achieved by introduction of a specific estimate()
callback for nft_hash_fast_ops which returns false for key lengths != 4.
In turn, nft_hash_estimate() is changed to return false for key lengths
== 4 so it won't be chosen by accident. Also, both callbacks must return
false for unbounded sets as their size estimate depends on a known
maximum element count.

Note that this patch partially reverts commit 4f2921ca21b71 ("netfilter:
nf_tables: meter: pick a set backend that supports updates") by making
nft_set_ops_candidate() not explicitly look for an update callback but
make NFT_SET_EVAL a regular backend feature flag which is checked along
with the others. This way all feature requirements are checked in one
go.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 15 insertions, 19 deletions

diff --git a/net/netfilter/nft_set_bitmap.c b/net/netfilter/nft_set_bitmap.c
index 45fb2752fb63..d6626e01c7ee 100644
--- a/net/netfilter/nft_set_bitmap.c
+++ b/net/netfilter/nft_set_bitmap.c
@@ -296,27 +296,23 @@ static bool nft_bitmap_estimate(const struct nft_set_desc *desc, u32 features,
 	return true;
 }
 
-static struct nft_set_type nft_bitmap_type;
-static struct nft_set_ops nft_bitmap_ops __read_mostly = {
-	.type		= &nft_bitmap_type,
-	.privsize	= nft_bitmap_privsize,
-	.elemsize	= offsetof(struct nft_bitmap_elem, ext),
-	.estimate	= nft_bitmap_estimate,
-	.init		= nft_bitmap_init,
-	.destroy	= nft_bitmap_destroy,
-	.insert		= nft_bitmap_insert,
-	.remove		= nft_bitmap_remove,
-	.deactivate	= nft_bitmap_deactivate,
-	.flush		= nft_bitmap_flush,
-	.activate	= nft_bitmap_activate,
-	.lookup		= nft_bitmap_lookup,
-	.walk		= nft_bitmap_walk,
-	.get		= nft_bitmap_get,
-};
-
 static struct nft_set_type nft_bitmap_type __read_mostly = {
-	.ops		= &nft_bitmap_ops,
 	.owner		= THIS_MODULE,
+	.ops		= {
+		.privsize	= nft_bitmap_privsize,
+		.elemsize	= offsetof(struct nft_bitmap_elem, ext),
+		.estimate	= nft_bitmap_estimate,
+		.init		= nft_bitmap_init,
+		.destroy	= nft_bitmap_destroy,
+		.insert		= nft_bitmap_insert,
+		.remove		= nft_bitmap_remove,
+		.deactivate	= nft_bitmap_deactivate,
+		.flush		= nft_bitmap_flush,
+		.activate	= nft_bitmap_activate,
+		.lookup		= nft_bitmap_lookup,
+		.walk		= nft_bitmap_walk,
+		.get		= nft_bitmap_get,
+	},
 };
 
 static int __init nft_bitmap_module_init(void)