netdev - Re: [PATCH net-next] bpf: add show

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Date:	Mon, 23 Nov 2015 20:12:19 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	John Fastabend <john.fastabend@...il.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	Daniel Borkmann <daniel@...earbox.net>, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] bpf: add show_fdinfo handler for maps

On Mon, Nov 23, 2015, at 20:09, John Fastabend wrote:
> On 15-11-23 10:03 AM, Alexei Starovoitov wrote:
> > On Mon, Nov 23, 2015 at 05:11:58PM +0100, Hannes Frederic Sowa wrote:
> >>
> >> Actually, that is the reason why I mentioned it, so *the admin* can see
> >> something is going on. Do you want to protect ebpf from root? Skynet? ;)
> > 
> > correct. To me both root and non-root are users in the first place and
> > they both shouldn't be allowed to misuse it.
> > 
> >> In my opinion the kernel never should hide any information of the admin
> >> if they are accessible easily. Sampling the number of failed updates to
> >> a map or printing it via procfs/ebpffs seems to be just a matter of how
> >> difficult it should be done. The map has a lock, so the number is fairly
> > 
> > map_lookup is actually lockless. It's a critical path and should be
> > as fast as possible. No extra stats just for debugging.
> > 
> >> accurate. Sampling and plotting size of hash maps without having kprobes
> >> installed would be a nice thing, because it reduces complexity and this
> >> is nice to have.
> > 
> > doing 'cat' from procfs is, of course, easier to use, but it's an extra
> > code that permenanetly lives in memory, whereas kprobe+bpf is a run-time
> > debugging.
> 
> Hopefully not jumping in off-base here (I've read most the thread), but
> what I've been doing is loading programs with debug ebpf code in them
> to keep a statistics map(s) and then I read that from  userspace for
> stats. It works pretty well and lets me compile out the debug code when
> I want and also doesn't need kprobe at all. Also I can implement
> sampling so that the debug code only runs every .01% or something like
> that so it can be used in "real" systems. My "real" systems are just a
> couple node test setup but it seems to be ok ;)

Ok, I am fine to wait until there is user demand.

Anyway, all you refer to is code you have under your control. I am
worried about bpf code that is not under my control.

Thanks,
Hannes
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