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, 9 insertions, 0 deletions

diff --git a/include/rule.h b/include/rule.h
index c232221e..ced63f3e 100644
--- a/include/rule.h
+++ b/include/rule.h
@@ -635,6 +635,8 @@ struct monitor {
 struct monitor *monitor_alloc(uint32_t format, uint32_t type, const char *event);
 void monitor_free(struct monitor *m);
 
+#define NFT_NLATTR_LOC_MAX 8
+
 /**
  * struct cmd - command statement
  *
@@ -666,6 +668,11 @@ struct cmd {
 		struct markup	*markup;
 		struct obj	*object;
 	};
+	struct {
+		uint16_t	offset;
+		struct location	*location;
+	} attr[NFT_NLATTR_LOC_MAX];
+	int			num_attrs;
 	const void		*arg;
 };
 
@@ -678,6 +685,8 @@ extern struct cmd *cmd_alloc_obj_ct(enum cmd_ops op, int type,
 				    const struct location *loc, struct obj *obj);
 extern void cmd_free(struct cmd *cmd);
 
+void cmd_add_loc(struct cmd *cmd, uint16_t offset, struct location *loc);
+
 #include <payload.h>
 #include <expression.h>