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

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Message-ID: <20151123180333.GB78190@ast-mbp.thefacebook.com>
Date:	Mon, 23 Nov 2015 10:03:34 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
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 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.

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