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

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Date:   Mon, 19 Feb 2018 14:08:15 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     code@...pl.cz
Cc:     netdev@...r.kernel.org, jiri@...nulli.us, xiyou.wangcong@...il.com,
        jbenc@...hat.com
Subject: Re: [PATCH] net: sched: report if filter is too large to dump

From: Roman Kapl <code@...pl.cz>
Date: Sun, 18 Feb 2018 23:10:47 +0100

> 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 -ENOMSG 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 don't see -ENOMSG used in your code, maybe you meant -EMSGSIZE.

> 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
> smaller SKBs in kernel.
> 
> Signed-off-by: Roman Kapl <code@...pl.cz>

Please do a little bit of research to seeh ow other subsystems
handle this situation, we should match whatever they do to be
consistent system wide with netlink.

You have to respin this patch to fix up the commit message anyways :-)

Thanks.