netdev - Re: [PATCH 2/7] mark root hnode explicitly

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Date:   Thu, 6 Sep 2018 19:57:25 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH 2/7] mark root hnode explicitly

On Thu, Sep 6, 2018 at 3:59 AM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
> index 3f985f29ef30..d14048e38b5c 100644
> --- a/net/sched/cls_u32.c
> +++ b/net/sched/cls_u32.c
> @@ -84,6 +84,7 @@ struct tc_u_hnode {
>         int                     refcnt;
>         unsigned int            divisor;
>         struct idr              handle_idr;
> +       bool                    is_root;
>         struct rcu_head         rcu;
>         u32                     flags;
>         /* The 'ht' field MUST be the last field in structure to allow for
> @@ -377,6 +378,7 @@ static int u32_init(struct tcf_proto *tp)
>         root_ht->refcnt++;
>         root_ht->handle = tp_c ? gen_new_htid(tp_c, root_ht) : 0x80000000;
>         root_ht->prio = tp->prio;
> +       root_ht->is_root = true;
>         idr_init(&root_ht->handle_idr);
>
>         if (tp_c == NULL) {
> @@ -693,7 +695,7 @@ static int u32_delete(struct tcf_proto *tp, void *arg, bool *last,
>                 goto out;
>         }
>
> -       if (root_ht == ht) {
> +       if (ht->is_root) {


What's wrong with comparing pointers with root ht?


>                 NL_SET_ERR_MSG_MOD(extack, "Not allowed to delete root node");
>                 return -EINVAL;
>         }
> @@ -795,6 +797,10 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
>                                 NL_SET_ERR_MSG_MOD(extack, "Link hash table not found");
>                                 return -EINVAL;
>                         }
> +                       if (ht_down->is_root) {

root ht is saved in tp->root, so you can compare ht_down with it too,
if you want.

If this check is all what you need, you don't need an extra flag.