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RE: [Xen-devel] Structure of the Xen source code

  • To: "Petersson, Mats" <Mats.Petersson@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Pradeep Singh, TLS-Chennai" <pradeep_s@xxxxxx>
  • Date: Tue, 20 Feb 2007 15:52:02 +0530
  • Delivery-date: Tue, 20 Feb 2007 02:26:17 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcdUMrLZPBqRLQ4JTBKoxnklKEMAywAAHHlQABr3orwAAHVVigANSV/gAAC9+n A=
  • Thread-topic: [Xen-devel] Structure of the Xen source code

-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx on behalf of Petersson, Mats
Sent: Tue 20-Feb-07 3:38 PM
To: Pradeep Singh, TLS-Chennai; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-devel] Structure of the Xen source code

> Depends on what you want to achieve... Understanding ALL of
> Xen is a LOT
> of effort. Understanding enough to be able to do what you
> need to do may
> be a lot less. What is the target of your "studying the code"?
> Target to understand how exactly Xen is booted and initialized.

Boot consists of:
Grub loads and decompresses Xen.gz + Linux-kernel [+ optional ramdisk +
optional security features]

It then jumps to the entry-point in xen.gz, which will do some
initialization before it jumps to the entry point of the Linux kernel
(Dom0 or "host").

Got it :)

> On second thought this is what i understood from my study.
> Xen binary sits with the patched xen dom0 kernel above hardware.
> Am i right?

Yes, that's pretty much it.
> When we say Xen binary i.e the first line of the Xen entry in
> Grub(e.g xen.gz), this is different from the patched dom0
> kernel, right?

Yes, those are two different binaries, with different purposes. Xen.gz
is the hypervisor, the linux kernel is a (modified) Linux operating
system kernel. The hypervisor is used by all guests (in this case Dom0
is also considered a guest, it's just a "special" guest).

> I look at this as
> xen.gz -> hypervisor
> linux.2.6.x.-xen.dom0 -> patched host kernel
> linux.2.6.x-xen.domU -> patched/unpatched guest kernel we
> want to boot.
If it's an "unpatched kernel" then it's not supplied in the source-code
of Xen. Unpatced kernels come from the guest-OS install CD (or similar).

As Daniel Stodden explained, there are also tools and other directorys
with "parts of Xen", including a documentation directory.

Thanks a lot for the help.



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