netdev - Re: [PATCH] xfrm: dst_entries_init() per-net dst

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Date:	Wed, 28 Oct 2015 11:09:09 -0400
From:	Dan Streetman <dan.streetman@...onical.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Steffen Klassert <steffen.klassert@...unet.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Dan Streetman <ddstreet@...e.org>
Subject: Re: [PATCH] xfrm: dst_entries_init() per-net dst_ops

On Wed, Oct 28, 2015 at 9:42 AM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
> Hello,
>
> On Wed, Oct 28, 2015, at 14:32, Dan Streetman wrote:
>> On Tue, Oct 27, 2015 at 12:15 PM,  <dan.streetman@...onical.com> wrote:
>> > From: Dan Streetman <dan.streetman@...onical.com>
>> >
>> > The ipv4 and ipv6 xfrms each create a template dst_ops object, and
>> > perform dst_entries_init() on the template objects.  Then each net
>> > namespace has its net.xfrm.xfrm[46]_dst_ops field set to the template
>> > values.  The problem with that is the dst_ops.pcpuc_entries field is
>> > a percpu counter and cannot be used correctly by simply copying it to
>> > another object.
>
> How hard would it be to split of the counters from the dst_ops struct?
> We could make dst_ops instances const and have normal pointers to them
> and keep the dst_entries as a small array in net namespace?

Well, the dst_ops->pcpuc_entries counter is used in dst.c which just
gets a struct dst_ops *, so it doesn't have access to the owning net
namespace.  And, not all dst_ops users have a per-net-namespace
dst_ops; ipv4/route.c for example uses a global "ipv4_dst_ops" object.
So it probably does need to stay owned by dst_ops.


>
> Bye,
> Hannes
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