Re: [nft PATCH v2 1/3] mnl: Support simple wildcards in netdev hooks

[Florian Westphal <fw@strlen.de>]

Phil Sutter <phil@nwl.cc> wrote:
> +		len = strlen(dev_array[0].ifname) + 1;
> +		if (dev_array[0].ifname[len - 2] == '*')
> +			len -= 2;

Not obvious to me, is there a guarantee that 'len' is 2?
And, what if len yields 0 here?

> +			if (dev_array[i].ifname[len - 2] == '*')
> +				len -= 2;
> +			mnl_attr_put(nlh, NFTA_DEVICE_NAME, len, dev_array[i].ifname);
>  			mnl_attr_nest_end(nlh, nest_dev);
>  		}
>  	}
> @@ -2084,14 +2090,17 @@ static void mnl_nft_ft_devs_build(struct nlmsghdr *nlh, struct cmd *cmd)
>  {
>  	const struct expr *dev_expr = cmd->flowtable->dev_expr;
>  	const struct nft_dev *dev_array;
> +	int i, len, num_devs = 0;
>  	struct nlattr *nest_dev;
> -	int i, num_devs= 0;
>  
>  	dev_array = nft_dev_array(dev_expr, &num_devs);
>  	nest_dev = mnl_attr_nest_start(nlh, NFTA_FLOWTABLE_HOOK_DEVS);
>  	for (i = 0; i < num_devs; i++) {
>  		cmd_add_loc(cmd, nlh, dev_array[i].location);
> -		mnl_attr_put_strz(nlh, NFTA_DEVICE_NAME, dev_array[i].ifname);
> +		len = strlen(dev_array[i].ifname) + 1;
> +		if (dev_array[i].ifname[len - 2] == '*')
> +			len -= 2;
> +		mnl_attr_put(nlh, NFTA_DEVICE_NAME, len, dev_array[i].ifname);

This (test, subtract, put) is a repeating pattern, perhaps this warrants a helper?