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



Patrick Colp wrote:

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.
Is that possible to find your version of xenstored in a tarball somewhere ?
attack.tar.gz seems to contains lots of things related to xenstored, but yet seems to missing watches and permissions.
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 haven't really had time to look yet (i've been swamped with others things), but will try to run your program. but what is dying in the scenario you described ? ocaml xenstored or the attack program ?
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?
libxenctrl is using the GPL license, whereas we chose the LGPL license with ocaml static exception everywhere.

--
Vincent

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