Re: [PATCH net-next 1/3] nexthop: Use a dedicated policy for nh_valid_get_del_req()

[Jakub Kicinski <kuba@kernel.org>]

On Mon, 18 Jan 2021 15:05:23 +0100 Petr Machata wrote:
> This function uses the global nexthop policy only to then bounce all
> arguments except for NHA_ID. Instead, just create a new policy that
> only includes the one allowed attribute.
> 
> Signed-off-by: Petr Machata <petrm@nvidia.com>
> Reviewed-by: Ido Schimmel <idosch@nvidia.com>
> ---
>  net/ipv4/nexthop.c | 21 ++++++---------------
>  1 file changed, 6 insertions(+), 15 deletions(-)
> 
> diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
> index e53e43aef785..d5d88f7c5c11 100644
> --- a/net/ipv4/nexthop.c
> +++ b/net/ipv4/nexthop.c
> @@ -36,6 +36,10 @@ static const struct nla_policy rtm_nh_policy[NHA_MAX + 1] = {
>  	[NHA_FDB]		= { .type = NLA_FLAG },
>  };
>  
> +static const struct nla_policy rtm_nh_policy_get[NHA_MAX + 1] = {

This is an unnecessary waste of memory if you ask me.

NHA_ID is 1, so we're creating an array of 10 extra NULL elements.

Can you leave the size to the compiler and use ARRAY_SIZE() below?

> +	[NHA_ID]		= { .type = NLA_U32 },
> +};
> +
>  static bool nexthop_notifiers_is_empty(struct net *net)
>  {
>  	return !net->nexthop.notifier_chain.head;
> @@ -1843,27 +1847,14 @@ static int nh_valid_get_del_req(struct nlmsghdr *nlh, u32 *id,
>  {
>  	struct nhmsg *nhm = nlmsg_data(nlh);
>  	struct nlattr *tb[NHA_MAX + 1];
> -	int err, i;
> +	int err;
>  
> -	err = nlmsg_parse(nlh, sizeof(*nhm), tb, NHA_MAX, rtm_nh_policy,
> +	err = nlmsg_parse(nlh, sizeof(*nhm), tb, NHA_MAX, rtm_nh_policy_get,
>  			  extack);
>  	if (err < 0)
>  		return err;
>  
>  	err = -EINVAL;
> -	for (i = 0; i < __NHA_MAX; ++i) {
> -		if (!tb[i])
> -			continue;
> -
> -		switch (i) {
> -		case NHA_ID:
> -			break;
> -		default:
> -			NL_SET_ERR_MSG_ATTR(extack, tb[i],
> -					    "Unexpected attribute in request");
> -			goto out;
> -		}
> -	}
>  	if (nhm->nh_protocol || nhm->resvd || nhm->nh_scope || nhm->nh_flags) {
>  		NL_SET_ERR_MSG(extack, "Invalid values in header");
>  		goto out;