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, 8 insertions, 0 deletions

diff --git a/src/rule.c b/src/rule.c
index 337a66bb..9307dad5 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -1377,6 +1377,14 @@ struct cmd *cmd_alloc(enum cmd_ops op, enum cmd_obj obj,
 	return cmd;
 }
 
+void cmd_add_loc(struct cmd *cmd, uint16_t offset, struct location *loc)
+{
+	assert(cmd->num_attrs < NFT_NLATTR_LOC_MAX);
+	cmd->attr[cmd->num_attrs].offset = offset;
+	cmd->attr[cmd->num_attrs].location = loc;
+	cmd->num_attrs++;
+}
+
 void nft_cmd_expand(struct cmd *cmd)
 {
 	struct list_head new_cmds;