linux-kernel - Re: [PATCH v2 1/2] net: sched: make default fifo qdiscs appear in the dump

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Date:   Wed, 8 Mar 2017 15:57:33 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Phil Sutter <phil@....cc>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] net: sched: make default fifo qdiscs appear in
 the dump

Wed, Mar 08, 2017 at 01:03:42PM CET, jikos@...nel.org wrote:
>From: Jiri Kosina <jkosina@...e.cz>
>
>The original reason [1] for having hidden qdiscs (potential scalability
>issues in qdisc_match_from_root() with single linked list in case of large
>amount of qdiscs) has been invalidated by 59cc1f61f0 ("net: sched: convert
>qdisc linked list to hashtable").
>
>This allows us for bringing more clarity and determinism into the dump by
>making default pfifo qdiscs visible.
>
>We're not turning this on by default though, at it was deemed [2] too
>intrusive / unnecessary change of default behavior towards userspace.
>Instead, TCA_DUMP_INVISIBLE netlink attribute is introduced, which allows
>applications to request complete qdisc hierarchy dump, including the
>ones that have always been implicit/invisible.
>
>Singleton noop_qdisc stays invisible, as teaching the whole infrastructure
>about singletons would require quite some surgery with very little gain
>(seeing no qdisc or seeing noop qdisc in the dump is probably setting
>the same user expectation).
>
>[1] http://lkml.kernel.org/r/1460732328.10638.74.camel@edumazet-glaptop3.roam.corp.google.com
>[2] http://lkml.kernel.org/r/20161021.105935.1907696543877061916.davem@davemloft.net
>
>Signed-off-by: Jiri Kosina <jkosina@...e.cz>
>---

[...]


>diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
>index 262f0379d83a..c7de00e09797 100644
>--- a/include/uapi/linux/rtnetlink.h
>+++ b/include/uapi/linux/rtnetlink.h
>@@ -542,6 +542,7 @@ enum {
> 	TCA_FCNT,
> 	TCA_STATS2,
> 	TCA_STAB,
>+	TCA_DUMP_INVISIBLE,
> 	TCA_PAD,

You are changing UAPI value of TCA_PAD...


> 	__TCA_MAX
> };