netdev - Re: [PATCH net-next 1/3] nexthop: Use a dedicated policy for nh_valid_get_del

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Date:   Tue, 19 Jan 2021 19:28:40 -0700
From:   David Ahern <dsahern@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>, Petr Machata <petrm@...dia.com>
Cc:     netdev@...r.kernel.org, David Ahern <dsahern@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next 1/3] nexthop: Use a dedicated policy for
 nh_valid_get_del_req()

On 1/19/21 1:55 PM, Jakub Kicinski wrote:
>> 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?

interesting suggestion in general for netlink attributes.

> 
>> +	[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];

This tb array too could be sized to just the highest indexed expected -
NHA_ID in this case.

>> -	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;
>