netdev - Re: [PATCH net-next 0/9] net: Kernel side filtering for route dumps

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Message-ID: <82e4fb1f-10b8-eda7-9643-36950e900103@gmail.com>
Date:   Thu, 11 Oct 2018 10:16:49 -0600
From:   David Ahern <dsahern@...il.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>,
        Sowmini Varadhan <sowmini.varadhan@...cle.com>,
        Stephen Hemminger <stephen@...workplumber.org>
Cc:     David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
        davem@...emloft.net
Subject: Re: [PATCH net-next 0/9] net: Kernel side filtering for route dumps

On 10/11/18 10:07 AM, Jamal Hadi Salim wrote:
> On 2018-10-11 11:46 a.m., Sowmini Varadhan wrote:
>> On (10/11/18 08:26), Stephen Hemminger wrote:
>>> You can do the something like this already with BPF socket filters.
>>> But writing BPF for multi-part messages is hard.
>>
>> Indeed. And I was just experimenting with this for ARP just last week.
>> So to handle the caes of "ip neigh show a.b.c.d" without walking through
>> the entire arp table and filtering in userspace, you could add a
>> sk_filter()
>> hook like this:
>>
> 
> If this could be done a lot earlier aka at xxx_fill_info() bpf would
> be a very good answer.

IMO, bpf at the fill_info stage is not appropriate.


> skb->sk (hence attached filter) should be available at that point.
> Classical bpf per Sowmini's example maybe trickier.
> Better - why dont we have an ebpf hook at this stage and then
> we dont have to make changes to the kernel when someone adds
> one more field to the filter?
> 
> BTW: useful for events as well - not just dumps (as the name
> fib_dump_filter suggests)

you mean kernel notifications on internal events?
1. there is no user socket when notifications are created and the
*_fill_info is invoked

2. notifications are global going to potentially many sockets. For these
cases the existing sk_filter is appropriate.