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Date:   Tue, 8 Oct 2019 16:00:49 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Christian Kellner <ckellner@redhat.com>,
        Christian Brauner <christian.brauner@ubuntu.com>
Cc:     linux-kernel@vger.kernel.org,
        Christian Kellner <christian@kellner.me>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Elena Reshetova <elena.reshetova@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Roman Gushchin <guro@fb.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "Dmitry V. Levin" <ldv@altlinux.org>
Subject: Re: [PATCH] pidfd: show pids for nested pid namespaces in fdinfo
Message-ID: <20191008140049.GM6681@dhcp22.suse.cz>
References: <20191008133641.23019-1-ckellner@redhat.com>
 <20191008135258.mzc7o2djiq5yydko@wittgenstein>
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On Tue 08-10-19 15:52:59, Christian Brauner wrote:
> On Tue, Oct 08, 2019 at 03:36:37PM +0200, Christian Kellner wrote:
> > From: Christian Kellner <christian@kellner.me>
> > 
> > The fdinfo file for a process file descriptor already contains the
> > pid of the process in the callers namespaces. Additionally, if pid
> > namespaces are configured, show the process ids of the process in
> > all nested namespaces in the same format as in the procfs status
> > file, i.e. "NSPid:\t%d\%d...". This allows the easy identification
> > of the processes in nested namespaces.
> > 
> > Signed-off-by: Christian Kellner <christian@kellner.me>
> 
> Yeah, makes sense to me.
> Note that if you send the pidfd to a sibling pid namespace NSpid won't
> show you anything useful. But that's what I'd expect security wise. You
> should only be able to snoop on descendant pid namespaces.
> 
> Please add a test for this to verify that this all works correctly and
> then resend. The tests live in tools/testing/selftests/pidfd/ and should
> already have most of the infrastructure there. The fdinfo parsing code
> should be in samples/pidfd/ which
> 
> For the patch itself:
> 
> Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
> 
> You can resend with my Reviewed-by retained if you don't change
> anything. Before I see tests I'll hold off on merging this. ;)

This is also forming a new user visible "api" right? So the make sure
that linux-api is on the Cc list.

And one minore note. The ifdefery is just ugly, could you just make it a
separate function with ifdef hidden inside?
-- 
Michal Hocko
SUSE Labs