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Re: [Xen-devel] [ANNOUNCE] xen ocaml tools



I've cleaned up the attack code (and added copy right info), Makefile, and README a bit for the attack. Please find the revised version attached.

Patrick


Patrick Colp wrote:
Vincent Hanquez wrote:
Patrick Colp wrote:
I'm really excited to see somebody else working on an OCaml XenStore! I was wondering if you could tell me what the difference are between this implementation and the one I recently released to the community?
this is a bit hard to tell without testing your version.

but i think the main difference is the way we handle transactions, which should provide a stable average time to commit transactions when having lots of xenstore traffic from guests.
I think you're thinking of my initial release last year. The version I 
released a few months ago also has an in-memory store and greatly 
improved transactions. It was motivated by the need to survive things 
like DoS attacks.
I wrote a little attack program (in OCaml) which runs from any DomU and 
brought the original xenstored to its knees. With the attack going, it's 
impossible to bring a new domain up -- it just hangs forever attempting 
to bring it up. Basically, the attack just hammers xenstored with 
micro-transactions. With the original transaction system, which allows 
the first committing transaction in a generation to win, long 
transactions could never complete. I implemented transactions that would 
enable all concurrent but non-conflicting transactions to commit. This 
made my version of xenstored resilient to the attack.
I played around with this with your version too, but found that, while 
it would not hang forever while attempting to load a domain, it would 
instead die after a few seconds with the following error:
Error: (2, 'No such file or directory')

I tried with with the eagain mode thing (random dropping of 1/3 of all transactions) both enabled and disabled, but it had the same effect (except that with the mode enabled, 1/3 of all transactions would fail regardless of if they should or not).
I've been reading over your code and noticed that you seem to have a 
mini-implementation of libxc. I was wondering why you chose to do this 
over using the pre-existing libxenctrl? Does this make the final 
executable smaller?

Patrick


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Attachment: attack.tar.gz
Description: GNU Zip compressed data

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