netdev - Re: [PATCH net-next v5] net: ip6mr: add RTM

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Date:   Fri, 8 Jul 2022 20:29:51 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     David Lamparter <equinox@...c24.net>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        David Ahern <dsahern@...nel.org>
Subject: Re: [PATCH net-next v5] net: ip6mr: add RTM_GETROUTE netlink op

Few more nit picks, sorry..

On Thu,  7 Jul 2022 11:33:36 +0200 David Lamparter wrote:
> +static int ip6mr_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
> +			      struct netlink_ext_ack *extack)
> +{
> +	struct net *net = sock_net(in_skb->sk);
> +	struct in6_addr src = {}, grp = {};
> +	struct nlattr *tb[RTA_MAX + 1];
> +	struct sk_buff *skb = NULL;

Should be unnecessary if the code is right, let the compiler warn us
about uninitialized variables.

> +	struct mfc6_cache *cache;
> +	struct mr_table *mrt;
> +	u32 tableid;
> +	int err;
> +
> +	err = ip6mr_rtm_valid_getroute_req(in_skb, nlh, tb, extack);
> +	if (err < 0)
> +		goto errout;

Can we:

		return err;

? I don't know where the preference for jumping to the return statement
came from, old compilers? someone's "gut feeling"?

> +	if (tb[RTA_SRC])
> +		src = nla_get_in6_addr(tb[RTA_SRC]);
> +	if (tb[RTA_DST])
> +		grp = nla_get_in6_addr(tb[RTA_DST]);
> +	tableid = tb[RTA_TABLE] ? nla_get_u32(tb[RTA_TABLE]) : 0;
> +
> +	mrt = ip6mr_get_table(net, tableid ? tableid : RT_TABLE_DEFAULT);

	tableid ? : RT_TABLE_DEFAULT

or

	tableid ?: RT_TABLE_DEFAULT

the abbreviated version of the ternary operator is used quite commonly
in the kernel.

> +	if (!mrt) {
> +		NL_SET_ERR_MSG_MOD(extack, "MR table does not exist");
> +		err = -ENOENT;
> +		goto errout_free;

Ditto, just return, if not goto errout; there's nothing to free.

> +	}
> +
> +	/* entries are added/deleted only under RTNL */
> +	rcu_read_lock();
> +	cache = ip6mr_cache_find(mrt, &src, &grp);
> +	rcu_read_unlock();
> +	if (!cache) {
> +		NL_SET_ERR_MSG_MOD(extack, "MR cache entry not found");
> +		err = -ENOENT;
> +		goto errout_free;
> +	}
> +
> +	skb = nlmsg_new(mr6_msgsize(false, mrt->maxvif), GFP_KERNEL);
> +	if (!skb) {
> +		err = -ENOBUFS;
> +		goto errout_free;
> +	}
> +
> +	err = ip6mr_fill_mroute(mrt, skb, NETLINK_CB(in_skb).portid,
> +				nlh->nlmsg_seq, cache, RTM_NEWROUTE, 0);
> +	if (err < 0)
> +		goto errout_free;

now this is the only case which actually needs to free the skb

> +
> +	err = rtnl_unicast(skb, net, NETLINK_CB(in_skb).portid);
> +
> +errout:
> +	return err;

when the label is gone you can:

	return rtnl_unicast(...

directly.

> +
> +errout_free:
> +	kfree_skb(skb);
> +	goto errout;

and no need to do the funky backwards jump here either, IMO

> +}