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Date:   Fri, 27 Jul 2018 16:19:36 +0200
From:   Florian Westphal <fw@strlen.de>
To:     Dmitry Safonov <dima@arista.com>
Cc:     Steffen Klassert <steffen.klassert@secunet.com>,
        Florian Westphal <fw@strlen.de>, linux-kernel@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Dmitry Safonov <0x7f454c46@gmail.com>, netdev@vger.kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        John Stultz <john.stultz@linaro.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
        linux-efi@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Shuah Khan <shuah@kernel.org>, linux-kselftest@vger.kernel.org,
        Eric Paris <eparis@redhat.com>,
        Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>,
        Pablo Neira Ayuso <pablo@netfilter.org>,
        Paul Moore <paul@paul-moore.com>, coreteam@netfilter.org,
        linux-audit@redhat.com, netfilter-devel@vger.kernel.org,
        Fan Du <fan.du@intel.com>
Subject: Re: [PATCH 00/18] xfrm: Add compat layer
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Dmitry Safonov <dima@arista.com> wrote:
> 1. It will double copy netlink messages, making it O(n) instead of
> O(1), where n - is number of bind()s.. Probably we don't care much.

About those bind() patches, I don't understand why they are needed.

Why can't you just add the compat skb to the native skb when doing
the multicast call?

skb_shinfo(skb)->frag_list = compat_skb;
xfrm_nlmsg_multicast(net, skb, 0, ...