Re: [Xen-users] Re: Xen and gnu gpl

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

On Monday 09 March 2009 23:23:49 Thomas Goirand wrote:
> Miles Fidelman wrote:
> > Thomas Goirand wrote:
> >> Mark Williamson wrote:
> >>> They did actually rewrite much of the userspace tools (Xend,
> >>> XenStored) themselves for their closed-source product
> >>
> >> Any idea what differences between the open source and the closed source
> >> version ? Why did they do such thing ?
> >
> > So they can make a living.

Well, that's part of it but Thomas is right in suspecting it's a bit more 
complicated.

Much of the user-facing "value add" from buying XenServer is that it has 
better management tools, either for a single server or for managing a cluster.  
They *could* get that by building on top of the APIs provided by the existing 
Xend.

> That I could guess, but I was wondering about the technical reasons ...

I'm not too clear on the specifics, sadly :-(

For Xend:
One simple reason could be that the codebase of Xend is not understood by many 
people - it is a fairly complex piece of code in its own right and was largely 
written by external contributors.  Another possible reason is that they may 
have wanted to add features that could not easily be added to the existing 
Xend architecture.

Finally, they may have just wanted to create a "better" Xend for purchasers of 
their software, as well as providing a better management interface, etc.

For XenStored:
Again, they may have wanted to add some kind of feature they didn't want in 
the OSS Xenstored (I think their Xenstored was required for the proprietary PV 
drivers for Windows to work, for instance).  Their Xenstored apparently also 
handles certain operations better, which makes it harder for malicious domains 
to abuse.

For both:
The rewrite of Xenstored and - I assume - Xend was in Ocaml, rather than 
Python.  Ocaml brings certain benefits (static typing, compilation, etc) over 
Python (which has benefits of its own).  Presumably they felt that Ocaml was a 
better language for this task.  Perhaps the programmers also had higher 
familiarity with it and were therefore able to produce better code more 
quickly.

Anyhow, that's my speculation on the matter.  I don't know the details but I 
doubt that there is *that* much difference between the two.  Much of XenServer 
*could* probably have been built on top of the existing Xend / Xenstored and 
these are all the technical / business reasons I can think of that they didn't 
do that.

They've Open Sourced the Ocaml Xenstored recently, so perhaps it will make its 
way into OSS Xen.

Cheers,
Mark

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