From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Rapoport <rppt@linux.ibm.com>
Subject: Re: [PATCH 1/1] userfaultfd: require CAP_SYS_PTRACE for
 UFFD_FEATURE_EVENT_FORK
Date: Thu, 7 Nov 2019 10:39:03 +0200
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To: Daniel Colascione <dancol@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>, Andy Lutomirski <luto@kernel.org>, linux-kernel <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Jann Horn <jannh@google.com>, Linus Torvalds <torvalds@linux-foundation.org>, Lokesh Gidra <lokeshgidra@google.com>, Nick Kralevich <nnk@google.com>, Nosh Minwalla <nosh@google.com>, Pavel Emelyanov <ovzxemul@gmail.com>, Tim Murray <timmurray@google.com>, Linux API <linux-api@vger.kernel.org>, linux-mm <linux-mm@kvack.org>
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Hi Daniel,

On Tue, Nov 05, 2019 at 08:41:18AM -0800, Daniel Colascione wrote:
> On Tue, Nov 5, 2019 at 8:24 AM Andrea Arcangeli <aarcange@redhat.com> wrote:
> > The long term plan is to introduce UFFD_FEATURE_EVENT_FORK2 feature
> > flag that uses the ioctl to receive the child uffd, it'll consume more
> > CPU, but it wouldn't require the PTRACE privilege anymore.
> 
> Why not just have callers retrieve FDs using recvmsg? This way, you
> retrieve the message packet and the file descriptor at the same time
> and you don't need any appreciable extra CPU use.

I don't follow you here. Can you elaborate on how recvmsg would be used in
this case?

-- 
Sincerely yours,
Mike.