From a43cc8d53096de069fab5d9bf1a2cc7b655c21c7 Mon Sep 17 00:00:00 2001
From: Pablo Neira Ayuso <pablo@netfilter.org>
Date: Tue, 6 Mar 2018 18:58:29 +0100
Subject: src: support for get element command

You need a Linux kernel >= 4.15 to use this feature.

This patch allows us to dump the content of an existing set.

 # nft list ruleset
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2, 3.3.3.3,
                             5.5.5.5-6.6.6.6 }
        }
 }

You check if a single element exists in the set:

 # nft get element x x { 1.1.1.5 }
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2 }
        }
 }

Output means '1.1.1.5' belongs to the '1.1.1.1-2.2.2.2' interval.

You can also check for intervals:

 # nft get element x x { 1.1.1.1-2.2.2.2 }
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2 }
        }
 }

If you try to check for an element that doesn't exist, an error is
displayed.

 # nft get element x x { 1.1.1.0 }
 Error: Could not receive set elements: No such file or directory
 get element x x { 1.1.1.0 }
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

You can also check for multiple elements in one go:

 # nft get element x x { 1.1.1.5, 5.5.5.10 }
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2, 5.5.5.5-6.6.6.6 }
        }
 }

You can also use this to fetch the existing timeout for specific
elements, in case you have a set with timeouts in place:

 # nft get element w z { 2.2.2.2 }
 table ip w {
        set z {
                type ipv4_addr
                timeout 30s
                elements = { 2.2.2.2 expires 17s }
        }
 }

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 include/mnl.h | 2 ++
 1 file changed, 2 insertions(+)

(limited to 'include/mnl.h')

diff --git a/include/mnl.h b/include/mnl.h
index 1b2450a9..d3eedeb7 100644
--- a/include/mnl.h
+++ b/include/mnl.h
@@ -79,6 +79,8 @@ int mnl_nft_setelem_batch_del(struct nftnl_set *nls, struct nftnl_batch *batch,
 int mnl_nft_setelem_batch_flush(struct nftnl_set *nls, struct nftnl_batch *batch,
 				unsigned int flags, uint32_t seqnum);
 int mnl_nft_setelem_get(struct netlink_ctx *ctx, struct nftnl_set *nls);
+struct nftnl_set *mnl_nft_setelem_get_one(struct netlink_ctx *ctx,
+					  struct nftnl_set *nls);
 
 struct nftnl_obj_list *mnl_nft_obj_dump(struct netlink_ctx *ctx, int family,
 					const char *table,
-- 
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