A little more clarification

[Ted Hilts <thilts@help-for-you.com>]

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Tim

Thank you for your comments.  I am still having a problem in trying to 
visualize a few things.  I hope you can persevere with me on this. Sorry 
to be so lengthy on something that seems more than obvious to others on 
the list. Let me explain.

Back in the days of Linux kernel 2.2.x I purchased VMWARE (for Linux) 
which was intended -- in non technical terms --  to be installed on top 
of or into my existing (SuSE 6.2 or 6.4 or equivalent installed 
distribution using kernel 2.2.x) Linux distribution. I just followed the 
instructions and it worked but I had no real insight into the matter. 
Then a few weeks ago a chap on the [SLE] list said he had downloaded Xen 
and installed it on top of or into his existing SuSE 9.1 (kernel 2.6.x) 
distribution installation. He indicated (just as with VMWARE) that he 
had a virtual Linux distribution installed on top of his existing or 
primary Linux installation. He indicated that both the initial 
installation and the virtual one ran concurrently. Although, that is 
probably not a techincally correct way of talking about these things. So 
when reading the tutorial and installation web pages for Xen I was 
predisposed to interpret this material from that same standpoint.  In 
otherwords, I either properly or improperly assumed that there must be a 
2.4.x or 2.6.x Linux system already up and working with the servers such 
as NFS, Telnet, SSH, portmap, and others as well the NIC and other 
physical interface devices all working.  In my mind it was this already 
installed and working distribution that would become the (basis) GUEST 
OS for DOMAIN 0 once the kernel was modified (ported) and installed 
becoming joined to Xen.

When I used VMWARE I just followed instructions but did not appreciate 
the reasoning or proprietary software architecture behind those 
instructions.  Because I now want to work with the source code of Xen 
and the Linux kernel I want very much to develop an accurate and proper 
insight. That is why I am now dwelling on this issue which was supposed 
to be my point #1 of 4 high level points in my previous email. So now I 
will ask my question.

Is what I have assumed correct, must there be an existing 2.4 or 2.6.x 
kernel based Linux installation up and running which must be modified 
(kernel modification or ported) to run Xen?  It is my understanding that 
the Xen source code installation or the binary installation both require 
a properly pre installed fully functional Linux system as the basis of 
Xen operation.  Once it's (pre installed linux distribution) 2.4.x or 
2.6.x kernel has been modified to work with the Xen software and tools 
we have created this Linux distribution into an Xen-based system called 
Domain 0 that becomes so when shutdown and then booted???

If my assuption correctly follows the Xen documentation then my first 
point should have read:

NOTE:: If this point is flawed by the assumpition that there must be a 
fully functional pre existing 2.4 or 2.6.x Linux sytem then my thinking 
is all screwed up. It would not be the first time. BTW, by OS I don't 
mean just the kernel. Some consider the entire installation the OS -- an 
obvious mutation.  I don't know how Xen documentation defines OS.  For 
some people the kernel is the OS as it is the primary layer.  For others 
the distribution less the desk top, games, graphical applications, 
office packages and any non command line controlled packages constitute 
the OS.  I use the latter definition.  So if OS means just the kernel 
code then  I will have to significantly change my point #1.

The following detail is what I meant to imply by my point #1.

#1 -- The BUILD:
The  Xen distribution includes 3 main components (Xen itself, ports of 
Linux 2.4 and 2.6.x kernels to run on (with) Xen, and user-space tools 
required to manage an Xen-based system) all of which assumes the 
existence of an already installed and fully fuctional  pre existing 
Linux system which must be adapted (to become the default Xen Linux 
build identified as DOMAIN 0.  Domain 0 is  the primary layer 
(controlled by the Xen package) and consists of the GUEST OS (the 
adapted pre existing Linux system) hosted by a secure pseudo virtual 
machine (a controlled execution environment using the adapted or ported 
kernel and Xen tools and processess to run and monitor parts of the 
GUEST OS (entire installed linux system?)).  The pre existing system 
once so adapted and running under Xen control contains support for 
relatively modern server-class network and disk hardware. The Xen 
process (called xend) runs in highest privilege in DOMAIN 0 and  it's 
code detects and starts secondary processors, sets up interrupt routing, 
time slicing, and performs PCI bus enumeration as well as offloads 
hardware support issues to DOMAIN 0 GUEST OS which is the modified pre 
existing Linux installed distribution.  As such, Xen provides a secure 
virtual machine for this GUEST OS, builds other domains using an OS 
installed in a root file system placed on a partition and booted from 
that partition, manages their virtual devices and performs 
administrative tasks.

My next question:
What exactly is an HTTP/S server -- apparently it is a requirement for 
browser administration access to a Xen-based system? Is Apache such a 
server and if not can it be turned into such a server???

One more question:
Regarding the source code.  I have been reviewing Python and C 
(gcc/gcc++) and was wondering if there was a high level diagram showing 
dependencies (hierarchy based on caller and called)  and code utilized 
(python, C, binary insertions, etc.)???

Based on what I am learning here (mostly from you) I have been 
constructing a very high level chart showing levels, key Xen processes, 
and stuff like that.  I will send you a copy once I am sure the 
information is correct and properly represents what is happening.

Thank you very much in advance for your comments and advice.

Ted



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