netdev - Re: [patch net-next v6 06/11] net: sched: use block index as a handle instead of qdisc when block is shared

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Date:   Sat, 6 Jan 2018 21:43:12 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, jhs@...atatu.com, xiyou.wangcong@...il.com,
        mlxsw@...lanox.com, andrew@...n.ch,
        vivien.didelot@...oirfairelinux.com, f.fainelli@...il.com,
        michael.chan@...adcom.com, ganeshgr@...lsio.com,
        saeedm@...lanox.com, matanb@...lanox.com, leonro@...lanox.com,
        idosch@...lanox.com, jakub.kicinski@...ronome.com,
        simon.horman@...ronome.com, pieter.jansenvanvuuren@...ronome.com,
        john.hurley@...ronome.com, alexander.h.duyck@...el.com,
        ogerlitz@...lanox.com, john.fastabend@...il.com,
        daniel@...earbox.net, dsahern@...il.com
Subject: Re: [patch net-next v6 06/11] net: sched: use block index as a
 handle instead of qdisc when block is shared

Sat, Jan 06, 2018 at 12:09:24AM CET, jiri@...nulli.us wrote:
>From: Jiri Pirko <jiri@...lanox.com>
>
>As the tcm_ifindex 0 is invalid ifindex, reuse it to indicate that we
>work with block, instead of qdisc. So if tcm_ifindex is 0, tcm_parent is
>used to carry block_index.
>
>If the block is set to be shared between at least 2 qdiscs, it is
>forbidden to use the qdisc handle to add/delete filters. In that case,
>userspace has to pass block_index.
>
>Also, for dump of the filters, in case the block is shared in between at
>least 2 qdiscs, the each filter is dumped with tcm_ifindex 0 and
>tcm_parent set to block_index. That gives the user clear indication,
>that the filter belongs to a shared block and not only to one qdisc
>under which it is dumped.
>
>Suggested-by: David Ahern <dsahern@...il.com>
>Signed-off-by: Jiri Pirko <jiri@...lanox.com>
>---

[...]

>@@ -886,8 +887,13 @@ static int tcf_fill_node(struct net *net, struct sk_buff *skb,
> 	tcm->tcm_family = AF_UNSPEC;
> 	tcm->tcm__pad1 = 0;
> 	tcm->tcm__pad2 = 0;
>-	tcm->tcm_ifindex = qdisc_dev(q)->ifindex;
>-	tcm->tcm_parent = parent;
>+	if (q) {
>+		tcm->tcm_ifindex = qdisc_dev(q)->ifindex;
>+		tcm->tcm_parent = parent;
>+	} else {
>+		tcm->tcm_ifindex = 0; /* block index is stored in parent */
>+		tcm->tcm_parent = block->index;
>+	}

Please guys, please look at this reuse (also on clt side). I would like
you to double-check this reuse of existing API for balock_index carrying
purpose. I believe it's UAPI safe. But please, check it out carefully.