netdev - Re: [PATCH 2/2] net: Implement SO_PASSCGROUP to enable passing cgroup path

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Date:	Tue, 15 Apr 2014 14:53:13 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	cgroups@...r.kernel.org,
	Network Development <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>, Tejun Heo <tj@...nel.org>,
	Simo Sorce <ssorce@...hat.com>, lpoetter@...hat.com,
	kay@...hat.com, dwalsh@...hat.com
Subject: Re: [PATCH 2/2] net: Implement SO_PASSCGROUP to enable passing cgroup path

On Tue, Apr 15, 2014 at 2:15 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
> This patch implements socket option SO_PASSCGROUP along the lines of
> SO_PASSCRED.
>
> If SO_PASSCGROUP is set, then recvmsg() will get a control message
> SCM_CGROUP which will contain the cgroup path of sender. This cgroup
> belongs to first mounted hierarchy in the sytem.
>
> SCM_CGROUP control message can only be received and sender can not send
> a SCM_CGROUP message. Kernel automatically generates one if receiver
> chooses to receive one.
>
> This works both for unix stream and datagram sockets.
>
> cgroup information is passed only if either the sender or receiver has
> SO_PASSCGROUP option set. This means for existing workloads they should
> not see any significant performance impact of this change.

This is odd.  Shouldn't an SCM_CGROUP cmsg be generated when the
receiver has SO_PASSCGROUP set and the sender passes SCM_CGROUP to
sendmsg?

--Andy
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