src: add comment support when adding tables

Adds userdata building logic if a comment is specified when creating a
new table. Adds netlink userdata parsing callback function.

Relies on kernel supporting userdata for nft_table.

Example:

> nft add table ip x { comment "test"\; }
> nft list ruleset

table ip x {
	comment "test"
}

Signed-off-by: Jose M. Guisado Gomez <guigom@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 15 insertions, 2 deletions

diff --git a/src/mnl.c b/src/mnl.c
index 388eff8f..cdcf9490 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -830,6 +830,7 @@ err:
 int mnl_nft_table_add(struct netlink_ctx *ctx, struct cmd *cmd,
 		      unsigned int flags)
 {
+	struct nftnl_udata_buf *udbuf;
 	struct nftnl_table *nlt;
 	struct nlmsghdr *nlh;
 
@@ -838,10 +839,22 @@ int mnl_nft_table_add(struct netlink_ctx *ctx, struct cmd *cmd,
 		memory_allocation_error();
 
 	nftnl_table_set_u32(nlt, NFTNL_TABLE_FAMILY, cmd->handle.family);
-	if (cmd->table)
+	if (cmd->table) {
 		nftnl_table_set_u32(nlt, NFTNL_TABLE_FLAGS, cmd->table->flags);
-	else
+
+		if (cmd->table->comment) {
+			udbuf = nftnl_udata_buf_alloc(NFT_USERDATA_MAXLEN);
+			if (!udbuf)
+				memory_allocation_error();
+			if (!nftnl_udata_put_strz(udbuf, NFTNL_UDATA_TABLE_COMMENT, cmd->table->comment))
+				memory_allocation_error();
+			nftnl_table_set_data(nlt, NFTNL_TABLE_USERDATA, nftnl_udata_buf_data(udbuf),
+					     nftnl_udata_buf_len(udbuf));
+			nftnl_udata_buf_free(udbuf);
+		}
+	} else {
 		nftnl_table_set_u32(nlt, NFTNL_TABLE_FLAGS, 0);
+	}
 
 	nlh = nftnl_nlmsg_build_hdr(nftnl_batch_buffer(ctx->batch),
 				    NFT_MSG_NEWTABLE,