netdev - Re: [PATCH net-next] net: sch: prio: Set bands to default on delete instead of noop

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Message-Id: <20180427.195639.1561525369470937297.davem@davemloft.net>
Date:   Fri, 27 Apr 2018 19:56:39 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     nogahf@...lanox.com
Cc:     netdev@...r.kernel.org, jiri@...nulli.us, jhs@...atatu.com,
        xiyou.wangcong@...il.com, mlxsw@...lanox.com
Subject: Re: [PATCH net-next] net: sch: prio: Set bands to default on
 delete instead of noop

From: Nogah Frankel <nogahf@...lanox.com>
Date: Thu, 26 Apr 2018 16:32:36 +0300

> When a band is created, it is set to the default qdisc, which is
> "invisible" pfifo.
> However, if a band is set to a qdisc that is later being deleted, it will
> be set to noop qdisc. This can cause a packet loss, while there is no clear
> user indication for it. ("invisible" qdisc are not being shown by default).
> This patch sets a band to the default qdisc, rather then the noop qdisc, on
> delete operation.
> 
> Signed-off-by: Nogah Frankel <nogahf@...lanox.com>

Like Cong, I'm worried this will break something.  The code has
behaved this way for 2 decades or longer.

If you want to put another qdisc there, and thus not drop any traffic,
modify the qdisc to a new one instead of performing a delete operation.