src: allow for updating devices on existing netdev chain

This patch allows you to add/remove devices to an existing chain:

 # cat ruleset.nft
 table netdev x {
	chain y {
		type filter hook ingress devices = { eth0 } priority 0; policy accept;
	}
 }
 # nft -f ruleset.nft
 # nft add chain netdev x y '{ devices = { eth1 };  }'
 # nft list ruleset
 table netdev x {
	chain y {
		type filter hook ingress devices = { eth0, eth1 } priority 0; policy accept;
	}
 }
 # nft delete chain netdev x y '{ devices = { eth0 }; }'
 # nft list ruleset
 table netdev x {
	chain y {
		type filter hook ingress devices = { eth1 } priority 0; policy accept;
	}
 }

This feature allows for creating an empty netdev chain, with no devices.
In such case, no packets are seen until a device is registered.

This patch includes extended netlink error reporting:

 # nft add chain netdev x y '{ devices = { x } ; }'
 Error: Could not process rule: No such file or directory
 add chain netdev x y { devices = { x } ; }
                                    ^

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/tests/shell/testcases/chains/netdev_chain_0 b/tests/shell/testcases/chains/netdev_chain_0
new file mode 100755
index 00000000..67cd715f
--- /dev/null
+++ b/tests/shell/testcases/chains/netdev_chain_0
@@ -0,0 +1,33 @@
+#!/bin/bash
+
+ip link add d0 type dummy || {
+        echo "Skipping, no dummy interface available"
+        exit 0
+}
+trap "ip link del d0" EXIT
+
+ip link add d1 type dummy || {
+        echo "Skipping, no dummy interface available"
+        exit 0
+}
+trap "ip link del d1" EXIT
+
+ip link add d2 type dummy || {
+        echo "Skipping, no dummy interface available"
+        exit 0
+}
+trap "ip link del d2" EXIT
+
+set -e
+
+RULESET="table netdev x {
+	chain y {
+		type filter hook ingress priority 0; policy accept;
+	}
+}"
+
+$NFT -f - <<< "$RULESET"
+
+$NFT add chain netdev x y '{ devices = { d0 }; }'
+$NFT add chain netdev x y '{ devices = { d1, d2, lo }; }'
+$NFT delete chain netdev x y '{ devices = { lo }; }'