netdev - Re: [PATCH v2 net-next 1/8] bpf: Add support for recursively running cgroup sock filters

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Date:   Thu, 31 Aug 2017 14:53:31 -0600
From:   David Ahern <dsahern@...il.com>
To:     Tejun Heo <tj@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     netdev@...r.kernel.org, daniel@...earbox.net, ast@...nel.org,
        davem@...emloft.net
Subject: Re: [PATCH v2 net-next 1/8] bpf: Add support for recursively running
 cgroup sock filters

On 8/31/17 8:22 AM, Tejun Heo wrote:
> On Sun, Aug 27, 2017 at 08:49:23AM -0600, David Ahern wrote:
>> On 8/25/17 8:49 PM, Alexei Starovoitov wrote:
>>>
>>>> +	if (prog && curr_recursive && !new_recursive)
>>>> +		/* if a parent has recursive prog attached, only
>>>> +		 * allow recursive programs in descendent cgroup
>>>> +		 */
>>>> +		return -EINVAL;
>>>> +
>>>>  	old_prog = cgrp->bpf.prog[type];
>>>
>>> ... I'm struggling to completely understand how it interacts
>>> with BPF_F_ALLOW_OVERRIDE.
>>
>> The 2 flags are completely independent. The existing override logic is
>> unchanged. If a program can not be overridden, then the new recursive
>> flag is irrelevant.
> 
> I'm not sure all four combo of the two flags makes sense.  Can't we
> have something simpler like the following?
> 
> 1. None: No further bpf programs allowed in the subtree.
> 
> 2. Overridable: If a sub-cgroup installs the same bpf program, this
>    one yields to that one.
> 
> 3. Recursive: If a sub-cgroup installs the same bpf program, that
>    cgroup program gets run in addition to this one.
> 
> Note that we can have combinations of overridables and recursives -
> both allow further programs in the sub-hierarchy and the only
> distinction is whether that specific program behaves when that
> happens.
> 

I am going to send v3 for patches 2-6 and 8 - the uncontested patches.

Alexei and I will meet in L.A. the week of Sept 11-15 to discuss the
recursive implementation (Patch 1 and its testing, patch 7).