[iptables PATCH v2 10/24] nft: Support fetch_chain_cache() per chain

[Phil Sutter]

Accept a specific chain's name to fetch from kernel. If given, prepare a
non-dump request with chain's table and name in payload. Kernel will
return only that chain (if it exists).

Signed-off-by: Phil Sutter <p...@nwl.cc>
---
 iptables/nft.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/iptables/nft.c b/iptables/nft.c
index 6ed05e77008c4..f116b940b41fd 100644
--- a/iptables/nft.c
+++ b/iptables/nft.c
@@ -1436,7 +1436,7 @@ static int fetch_table_cache(struct nft_handle *h)
 }
 
 static int fetch_chain_cache(struct nft_handle *h,
-                            const struct builtin_table *t)
+                            const struct builtin_table *t, const char *chain)
 {
        struct nftnl_chain_list_cb_data d = {
                .h = h,
@@ -1461,12 +1461,24 @@ static int fetch_chain_cache(struct nft_handle *h,
                }
        } else if (!h->cache->table[t->type].chains) {
                h->cache->table[t->type].chains = nftnl_chain_list_alloc();
-       } else {
-               return 0;
        }
 
-       nlh = nftnl_chain_nlmsg_build_hdr(buf, NFT_MSG_GETCHAIN, h->family,
-                                       NLM_F_DUMP, h->seq);
+       if (t && chain) {
+               struct nftnl_chain *c = nftnl_chain_alloc();
+
+               if (!c)
+                       return -1;
+
+               nlh = nftnl_chain_nlmsg_build_hdr(buf, NFT_MSG_GETCHAIN, 
h->family,
+                                                 NLM_F_ACK, h->seq);
+               nftnl_chain_set_str(c, NFTNL_CHAIN_TABLE, t->name);
+               nftnl_chain_set_str(c, NFTNL_CHAIN_NAME, chain);
+               nftnl_chain_nlmsg_build_payload(nlh, c);
+               nftnl_chain_free(c);
+       } else {
+               nlh = nftnl_chain_nlmsg_build_hdr(buf, NFT_MSG_GETCHAIN, 
h->family,
+                                               NLM_F_DUMP, h->seq);
+       }
 
        ret = mnl_talk(h, nlh, nftnl_chain_list_cb, &d);
        if (ret < 0 && errno == EINTR)
@@ -1639,7 +1651,7 @@ static void __nft_build_cache(struct nft_handle *h)
 
 retry:
        mnl_genid_get(h, &genid_start);
-       fetch_chain_cache(h, NULL);
+       fetch_chain_cache(h, NULL, NULL);
        fetch_rule_cache(h, NULL);
        h->have_cache = true;
        mnl_genid_get(h, &genid_stop);
@@ -1709,7 +1721,7 @@ struct nftnl_chain_list *nft_chain_list_get(struct 
nft_handle *h,
                return NULL;
 
        if (!h->have_cache && !h->cache->table[t->type].chains)
-               fetch_chain_cache(h, t);
+               fetch_chain_cache(h, t, NULL);
 
        return h->cache->table[t->type].chains;
 }
-- 
2.23.0