Re: Libvir: a simple C virtualization control library

[Anthony Liguori <aliguori@us.ibm.com>]

Hi Daniel,

I think the goal of having a library that allows applications to 
interact with Xen is a great idea.

I suggest though that instead of taking the current approach of 
reimplementing a hypercall library, you consider just using Xend's HTTP 
interface.

xm/xend communicate via an web services API that's based on 
S-Expressions.  Xend can listen on a domain socket and/or a TCP socket 
for incoming connections so both transports should be supported.

You can access this interface by doing an HTTP request with the 
Content-Type set to application/sxp.  The protocol uses the URL to 
identify the command and options and returns s-expressions.  You can get 
a feeling for the supported commands by enabling the TCP server and 
going to http://localhost:8000/xend/domain/

This would allow you to have an LGPL control library yet not rewrite all 
of Xend.  It also requires minimal dependencies since I believe libxml2 
already has an HTTP client (though you'd have to add a domain socket 
transport).

An interesting thing to do too would be to attempt to add support to 
Xend for another mime type (like text/xml) and perhaps even support 
XML-RPC.  This would be really excellent long term as it could eliminate 
a ton of code in Xend and xm by just reusing the python XML-RPC support.

Regards,

Anthony Liguori

Daniel Veillard wrote:

>  This mail is to present a new project being started:
>
>       Libvir: a simple C virtualization control library
>
> The libvir library is born from the need for a simpler userland C library
>to watch and control Xen domains. Among the design goal are:
>
>   - being able to provide API and ABI guarantee
>   - LGPL to be able to use it in a variety of contexts
>   - pure C, minimizing dependancies
>   - aiming at full documentation coverage
>
> A typical example of use case should be the applet displaying local Xen
>domains status in Fedora Core desktop.
>
> The current state is a small library to get informations and interract
>with existing domains, the design is not frozen, though the existing code
>should work as is, it is considered mostly as a way to bootstrap and
>seed the project, we are seeking interest from others. The library could
>be extended in various ways potentally supporting other virtualization
>mechanisms like QEmu, allowing to start new domains, etc. as long as the
>API is kept simple enough.
>
> The project is hosted at :
>     http://libvir.org/
>API  http://libvir.org/html/libvir-libvir.html
>
>See the download page at http://libvir.org/downloads.html to get sources
>or CVS checkout, and https://www.redhat.com/mailman/listinfo/libvir-list
>for the mailing-list informations, which would be the best place to discuss
>this for those interested in this project,
>
>   yours,
>
>Daniel
>
>  
>