netdev - Re: [PATCH v2] sched: report if filter is too large to dump

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Message-ID: <20180221074554.GE4196@orbyte.nwl.cc>
Date:   Wed, 21 Feb 2018 08:45:54 +0100
From:   Phil Sutter <phil@....cc>
To:     Roman Kapl <code@...pl.cz>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Jiri Pirko <jiri@...nulli.us>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Benc <jbenc@...hat.com>
Subject: Re: [PATCH v2] sched: report if filter is too large to dump

Hi Roman,

On Mon, Feb 19, 2018 at 09:32:51PM +0100, Roman Kapl wrote:
> So far, if the filter was too large to fit in the allocated skb, the
> kernel did not return any error and stopped dumping. Modify the dumper
> so that it returns -EMSGSIZE when a filter fails to dump and it is the
> first filter in the skb. If we are not first, we will get a next chance
> with more room.
> 
> I understand this is pretty near to being an API change, but the
> original design (silent truncation) can be considered a bug.
> 
> Note: The error case can happen pretty easily if you create a filter
> with 32 actions and have 4kb pages. Also recent versions of iproute try
> to be clever with their buffer allocation size, which in turn leads to

I'm curious, what does it lead to? :)

Thanks, Phil