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Re: [Libvir] XML-RPC support for libvirt

On Fri, Mar 10, 2006 at 10:57:59AM -0600, Anthony Liguori wrote:
> Howdy,

  Evening ;-)

> I'm about to checkin some XML-RPC code into CVS.  The code I'm checking 

  okay got it. Please add a Changelog entry when you commit to the base :-)

> in won't compile by default (for now) as there's still a little work to 
> do but I wanted to get something into the tree.  Here are the tasks left:
> 1) Convert from dict to s-expressions to handle config returns.  Right 
> now, the Xend XML-RPC code returns S-Expressions in the form of a 
> tuple.  We just need a little code to convert from these tuples to 
> struct sexpr's.
> 2) Integrate my unit tests.  I've got a number of unit tests that stress 
> the various bits of parsing code.  I'd like to add a make check that 
> runs these unit tests and a make fullcheck that runs these unit tests 
> under valgrind.
> 3) Support XML-RPC over a domain socket.  Right now I'm using nanohttp 
> which doesn't appear to allow different transports.  There is some HTTP 
> PUT code already in the tree so I could use that if there isn't a more 
> clever solution.
> 4) Plumb the xend backend functions to XML-RPC.  This is really straight 
> forward.  It's just a matter of converting:
> int
> xend_pause(virConnectPtr xend, const char *name)
> {
>    return xend_op(xend, name, "op", "pause", NULL);
> }
> To:
> int
> xend_pause(virConnectPtr xend, const char *name)
> {
>    if (xend->xmlrpc)
>        return xmlRpcCall(xend->xmlrpc, "xend.domain.pause", "", "s", name)
>    else
>        return xend_op(xend, name, "op", "pause", NULL);
> }

  Okay the steps needed look fairly clear, thanks :-)

> Of course, using the xml-rpc code, we now have access to rich fault 
> information.  Xend never actually returns errors for things and instead 
> throws exceptions.

  the new error code tries at least to extract the error message when
an HTTP POST or GEt fails with an error code, but the XML-RPC should 
give a far more reliable framework for error handling.

> For the S-Expression/HTTP protocol, you just get a 
> 501 and have to return a meaningless error.  With XML-RPC, those 
> exceptions are actually serialized and sent over the wire.  We may want 
> to explore how we can make that information available to the user.

  I would say as a buffer at least that's no problem. But exposing 
the structure of the error stack on the server may be a bit too much.

> My current understanding, btw, is that the basic XML-RPC support for 
> Xend is going into the tree sometime this week (Ewan is looking at the 
> code now) and will be a part of the 3.0.2 release.  This means that for 

  That's waht I was told too :-)

> the 3.0.3 cycle, we'll be defining a standard API.  This process will be 
> starting soon (within the next couple of weeks hopefully).

  Excellent ! Good good !
Hopefully we will be able to confront that with what is present in other
engines like l4 and QEmu and make sure at least for the 'common' APIs
the semantic is similar.


Daniel Veillard      | Red Hat http://redhat.com/
veillard redhat com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/

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