netdev - Re: [RFC PATCH 3/5] bpf: add BPF_PROG_ATTACH and BPF_PROG

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Message-ID: <20160817174813.GA98226@ast-mbp.thefacebook.com>
Date:	Wed, 17 Aug 2016 10:48:14 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Daniel Mack <daniel@...que.org>
Cc:	Tejun Heo <htejun@...com>, daniel@...earbox.net, ast@...com,
	davem@...emloft.net, kafai@...com, fw@...len.de,
	pablo@...filter.org, harald@...hat.com, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 3/5] bpf: add BPF_PROG_ATTACH and BPF_PROG_DETACH
 commands

On Wed, Aug 17, 2016 at 05:51:44PM +0200, Daniel Mack wrote:
> On 08/17/2016 05:06 PM, Tejun Heo wrote:
> > What I'd suggest is keeping two sets of pointers, one set for the
> > programs explicitly attached to the cgroup and the other for programs
> > which are to be executed for the cgroup.  The two pointers in the
> > latter set will point to the closest non-null program in its ancestry.
> > Note that the pointers may point to programs belonging to different
> > ancestors.
> > 
> > 	A - B - C
> >               \ D - E
> > 
> > Let's say B has both ingress and egress programs and D only has
> > egress.  E's execution pointers should point to D's egress program and
> > B's ingress program.
> > 
> > The pointers would need to be updated
> > 
> > 1. When a program is installed or removed.  For simplicity's sake, we
> >    can just walk the whole hierarchy.  If that's too expensive
> >    (shouldn't be), we can find out the closest ancestor where both
> >    programs can be determined and then walk from there.
> > 
> > 2. When a new cgroup is created, it should inherit its execution table
> >    from its parent.
> 
> Ok, yes, that sounds sane to me. Will implement that scheme.

That makes sense to me as well. Sounds quite flexible and fast
with only one check per packet per direction.