netdev - Re: [patch iproute2 v8 1/2] lib/libnetlink: Add functions rtnl_talk_msg and rtnl_talk

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Date:   Thu, 11 Jan 2018 16:08:53 +0100
From:   Phil Sutter <phil@....cc>
To:     David Ahern <dsahern@...il.com>, Chris Mi <chrism@...lanox.com>,
        netdev@...r.kernel.org, gerlitz.or@...il.com,
        stephen@...workplumber.org, marcelo.leitner@...il.com
Subject: Re: [patch iproute2 v8 1/2] lib/libnetlink: Add functions
 rtnl_talk_msg and rtnl_talk_iov

On Wed, Jan 10, 2018 at 09:12:45PM +0100, Phil Sutter wrote:
> On Wed, Jan 10, 2018 at 12:20:36PM -0700, David Ahern wrote:
> [...]
> > 2. I am using a batch file with drop filters:
> > 
> > filter add dev eth2 ingress protocol ip pref 273 flower dst_ip
> > 192.168.253.0/16 action drop
> > 
> > and for each command tc is trying to dlopen m_drop.so:
> > 
> > open("/usr/lib/tc//m_drop.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such
> > file or directory)
> 
> [...]
> 
> > Can you look at a follow on patch (not part of this set) to cache status
> > of dlopen attempts?
> 
> IMHO the logic used in get_action_kind() for gact is the culprit here:
> After trying to dlopen m_drop.so, it dlopens m_gact.so although it is
> present already. (Unless I missed something.)

Not quite, m_gact.c is statically compiled in and there is logic around
dlopen(NULL, ...) to prevent calling it twice.

> I guess the better (and easier) fix would be to create some more struct
> action_util instances in m_gact.c for the primitives it supports so that
> the lookup in action_list succeeds for consecutive uses. Note that
> parse_gact() even supports this already.

Sadly, this doesn't fly: If a lookup for action 'drop' is successful,
that value is set as TCA_ACT_KIND and the kernel doesn't know about it.

I came up with an alternative solution, what do you think about attached
patch?

Thanks, Phil

View attachment "dlopen_gact.diff" of type "text/plain" (1650 bytes)