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Re: [Xen-devel] a last comment on xml-rpc

To: Ronald G Minnich <rminnich@xxxxxxxx>
Subject: Re: [Xen-devel] a last comment on xml-rpc
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Fri, 10 Feb 2006 17:38:31 -0600
Cc: Matt Sottile <matt@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Ronald G Minnich wrote:
I think Xen made the right decision, in the beginning, to use s-exprs. We have heard from any number of places that learned the hard way that XML is a really poor foundation for RPC.

I hope you will reconsider going to XML-RPC. I don't think the existence of python support is sufficient. The whole point of RPC, in fact, is to let any client talk to any server, without regard to language or environment. We know in practice that trivial C programs can use s-expression based RPC; we've seen how awful the XML parsers in C can be; do you really want to lock C out of this picture?
I don't think that's fair at all. I've written the C code to interface with Xend using S-Expression/HTTP and it's painful (see libvirt).

I've also written an XML-RPC interface to Xend in C using libxml2. It very little code and just works. Granted, parsing XML is more painful that parsing S-Expressions but there are so many libraries for so many languages that XML parsing is really a nop.

I don't see any point in rolling out our own RPC mechanism when a standard one exists that is well supported in most languages. There is also a C library that provides support for XML-RPC (libxmlrpc_c) so interfacing with Xend using C would require no additional code on the client side. All the major high level languages I know of have XML-RPC support as part of the standard library.

We're talking about a pretty significant reduction in code in Xend too by moving to XML-RPC. If Python supported a different RPC mechanism I would support moving to that simply to reduce the complexity of Xend.


Anthony Liguori


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