RE: various questions

[Dave Scott <Dave.Scott@xxxxxxxxxxxxx>]

Hi,

[cc:d xen-api@xxxxxxxxxxxxx where xen-api/xen-api-libs are developed]

Charalampos Rotsos wrote:

> Hi all, 

> As a quick intro, over  summer I have been working on getting mirage
> to work as a network simulation and emulation platform. I have developed
> so far an ns3 backend tha allow to run applications as event driven
> simulations and a mechanism to bootstrap distributed xen-based emulation
> using the xapi interface. Also, because this work was focused to develop
> a tool that allow to understand the impact of sdn network architectures,
> I have develop a number of openflow and traffic generation libraries. So
> far the work is done on the old mirage tree and I will try to port my
> work into the main mirage-platform tools in the near future. 

This sounds really interesting!

> I am currently trying to get a first cut of the xen emulation task and I
> have a couple of question over various things: 

> 1) In order to install the xapi libraries, I need to install a number of
> libraries, that they are different from the libraries distributed by opam.
> The problem is that some of the libraries use some very weird installation
> mechanisms. The xen people have solved the problem by distributed a hacked
> version of these libraries through https://github.com/xen-org/xen-api-libs/.
> How can I introduce an opam recipe in the opam repo that will notify the
> installation mechanism that the libraries are available through this repo
> and override the default recipes for the specific libraries? I tries also
> to rewrite the default recipes for some libraries but I got stuck on
> finding a way to generate a custom META file and I gave up. 

The long-term plan for xen-api-libs is to use the upstream packages instead
of entirely custom ones. For example, now that "ocaml-rpc" is available
through opam I'd like to remove the custom fork "xen-api-libs/rpc-light".

Some of the code in "xen-api-libs" is a (not very high quality IMHO) custom
"standard library". I think we should probably switch to a better alternative,
such as (Jane Street) Core. However in the short term we could probably just
opam-package what we have.

Which particular packages are you having trouble with? I could take a quick
look and see if I could help.

Also, if you're running debian you might be able to just use "apt" to fetch
the build dependencies of xapi in your opam "system" compiler.

> 2) For the ocaml-pcap library is there some example code and the device
> configurations I need in order to get it working as a network capture
> mechanism for a xen vm? 

The extra pieces are:

1. mirage-net netif support for capture

https://github.com/mirage/mirage-net/pull/5

(I just made the pull request)

2. a bit of glue to read the captured frames and write them to a block
device. I'm half-way through a bit of refactoring -- I'll send you a link
when I'm done.

> 3) I have written some code that allows to generate network topologies and
> boot vm over xapi and I have tested and verified the code on a debian vm.
> This unfortunately is constrained on testing the network throttling
> configurations. Is there any xapi configured machine I could get access to
> to verify the runtime correctnesss of the code? 

When you say "network throttling" do you mean netback VIF rate limiting? If
so there is a bug against the xen-api master branch and a fix in a pull
request.

Cheers,
Dave