xtables-restore: Minimize caching when flushing

Unless --noflush was given, xtables-restore merely needs the list of
tables to decide whether to delete it or not. Introduce nft_fake_cache()
function which populates table list, initializes chain lists (so
nft_chain_list_get() returns an empty list instead of NULL) and sets
'have_cache' to turn any later calls to nft_build_cache() into nops.

If --noflush was given, call nft_build_cache() just once instead of for
each table line in input.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Acked-by: Florian Westphal <fw@strlen.de>

1 files changed, 17 insertions, 0 deletions

diff --git a/iptables/nft.c b/iptables/nft.c
index fde1b2a3..a2f36b7e 100644
--- a/iptables/nft.c
+++ b/iptables/nft.c
@@ -1611,6 +1611,23 @@ retry:
 	h->nft_genid = genid_start;
 }
 
+void nft_fake_cache(struct nft_handle *h)
+{
+	int i;
+
+	fetch_table_cache(h);
+	for (i = 0; i < NFT_TABLE_MAX; i++) {
+		enum nft_table_type type = h->tables[i].type;
+
+		if (!h->tables[i].name)
+			continue;
+
+		h->cache->table[type].chains = nftnl_chain_list_alloc();
+	}
+	h->have_cache = true;
+	mnl_genid_get(h, &h->nft_genid);
+}
+
 void nft_build_cache(struct nft_handle *h)
 {
 	if (!h->have_cache)