netdev - Re: [Patch 1/1][RFC] NETDEV: Find network bugs by validating the sk

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Date:	Thu, 30 Apr 2009 10:59:13 -0700
From:	David VomLehn <dvomlehn@...co.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [Patch 1/1][RFC] NETDEV: Find network bugs by validating the
	sk_buff state

On Thu, Apr 30, 2009 at 09:46:14AM -0700, David Miller wrote:
> From: David VomLehn <dvomlehn@...co.com>
> Date: Thu, 30 Apr 2009 09:32:00 -0700
> 
> > I think the size is very doable. Only two bits are needed to encode
> > the state so the ability to check the state isn't an issue. The
> > other piece, though, is recording enough information to be able to
> > pinpoint the problem.
> 
> It's not my job to design this thing for you, but I guess that's what
> I have to do to get you to think out of the box a little bit :-/

Uh, perhaps you missed the rest of the email, where I said I'm thinking of
a couple of approaches. The purpose of the email was to let you know briefly
that I am looking at approaches that will meet your 16-bit space constraint.

> Maintain a table, which is only recorded into when the debugging
> feature is enable (via sysctl or whatever) which remembers this stuff.
> 
> That way nobody eats the space or time overhead unless the debugging
> feature is enabled.

Your description is general enough that I may misunderstand your idea,
but it sounds like, if debugging was on, you'd be recording every call to
alloc_skb and kfree_skb in your table. This would use a lot of memory.
You can't simply have a circular list, because an sk_buff might be allocated
for a very long time before being used and you would overwrite its entry.
This would reduce the reliability of the information, which is the last thing
you want in a debugging tool. So, I'm considering approaches without this
drawback.

> Wow, I had to use every brain cell I have to come up with that one!

David VomLehn
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