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RE: [Xen-devel] XAPI source code

To: 'Huibin QIAN' <qianhb@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] XAPI source code
From: Dave Scott <Dave.Scott@xxxxxxxxxxxxx>
Date: Tue, 22 Dec 2009 11:02:31 +0000
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Thread-topic: [Xen-devel] XAPI source code

> Hi All
> I have downloaded the opensource xapi source code. I am not sure what the 
> functins of the follow modules:
>  1 block_device_io

This contains code to store a "redo log" directly on a shared block device. If 
this is enabled and the Pool master crashes, none 
of the metadata updates will be lost.

>  2 datamodel

This is a combination of an IDL for the XenAPI and a database schema for the 

>  3 xiu (I am puzzled by the name "xiu")

It originally stood for 'xen in userspace'. It's a hypercall simulator-- it 
allows the toolstack to be run inside a small VM without talking to a real 
hypervisor or starting real domains. It allows large pools to be simulated 
efficiently without having to nest hypervisors.

>  4 stats

This isn't very important. We use this to compute simple aggregate statistics 
e.g. the length of the 'blackout' interval during a live migrate. I'm not sure 
how useful these numbers really are.
>  5 rpc-light

In xen-api-libs.hg this provides a nice way to autogenerate value 
marshalling/unmarshalling code directly from ocaml datatypes (via ocamlp4). 
There are currently JSON and XMLRPC 'backends' and it's easy to add new ones.

>  6 rss

An unused module which can generate RSS feeds.

>  7 xb (I think the xapi needs not to talk to xenbus directly)

This is used by the 'xs' library to talk to xenstore. Note that xapi doesn't 
use libxenstore.

>  8 xsrpc (why it writes some "rpc" keys to path of "domain/<domid>" in the 

This is an old prototype of a xenstore RPC mechanism. In future we'll probably 
add backends to 'rpc-light' instead of using this module. That way it's easier 
to change the concrete data format (e.g. to use shared memory or something)


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