src: initial extended netlink error reporting

This patch correlates the in-kernel extended netlink error offset and
the location information.

Assuming 'foo' table does not exist, then error reporting shows:

 # nft delete table foo
 Error: Could not process rule: No such file or directory
 delete table foo
              ^^^

Similarly, if table uniquely identified by handle '1234' does not exist,
then error reporting shows:

 # nft delete table handle 1234
 Error: Could not process rule: No such file or directory
 delete table handle 1234
                     ^^^^

 Assuming 'bar' chain does not exists in the kernel, while 'foo' does:

 # nft delete chain foo bar
 Error: Could not process rule: No such file or directory
 delete chain foo bar
                  ^^^

 This also gives us a hint when adding rules:

 # nft add rule ip foo bar counter
 Error: Could not process rule: No such file or directory
 add rule ip foo bar counter
             ^^^

This is based on ("src: basic support for extended netlink errors") from
Florian Westphal, posted in 2018, with no netlink offset correlation
support.

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

1 files changed, 20 insertions, 0 deletions

diff --git a/include/netlink.h b/include/netlink.h
index d02533ec..c2eb8949 100644
--- a/include/netlink.h
+++ b/include/netlink.h
@@ -16,6 +16,22 @@
 
 #define MAX_REGS	(1 + NFT_REG32_15 - NFT_REG32_00)
 
+#ifndef NETLINK_EXT_ACK
+#define NETLINK_EXT_ACK                 11
+
+enum nlmsgerr_attrs {
+	NLMSGERR_ATTR_UNUSED,
+	NLMSGERR_ATTR_MSG,
+	NLMSGERR_ATTR_OFFS,
+	NLMSGERR_ATTR_COOKIE,
+
+	__NLMSGERR_ATTR_MAX,
+	NLMSGERR_ATTR_MAX = __NLMSGERR_ATTR_MAX - 1
+};
+#define NLM_F_CAPPED	0x100	/* request was capped */
+#define NLM_F_ACK_TLVS	0x200	/* extended ACK TVLs were included */
+#endif
+
 struct netlink_parse_ctx {
 	struct list_head	*msgs;
 	struct table		*table;
@@ -176,6 +192,10 @@ struct netlink_mon_handler {
 
 extern int netlink_monitor(struct netlink_mon_handler *monhandler,
 			    struct mnl_socket *nf_sock);
+struct netlink_cb_data {
+	struct netlink_ctx	*nl_ctx;
+	struct list_head	*err_list;
+};
 int netlink_echo_callback(const struct nlmsghdr *nlh, void *data);
 
 struct ruleset_parse {