WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] What are the differences between the boot of Xen and Lin

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] What are the differences between the boot of Xen and Linux Kernel
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Fri, 11 Jul 2008 16:02:19 +0100
Cc: Tom Creck <tom-xen@xxxxxxxxxxx>
Delivery-date: Fri, 11 Jul 2008 08:02:50 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <18377629.post@xxxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <18377629.post@xxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: KMail/1.9.9
Hello,

>          As the Xen hypervisor can be treated as a microkernel, what are
> the differences between the boot of Xen hypervisor and a traditional native
> linux kernel?

Xen is booted using multiboot, which means that Grub has already set up 
protected mode for it.  I'm not sure if Linux ever uses multiboot but it 
certainly doesn't have to, in which case it may do a load of realmode stuff 
that isn't necessary for Xen.

After that, they'll both have to go through some basic gyrations to gather 
information about the machine (its memory structure, SMP configuration, etc) 
and activate paging.  I'm not sure how much commonality there is in the code 
here.  I've not looked at it for ages.

Once initial machine setup is done, there's quite a big difference: Linux will 
need to set up a whole load of device drivers, start a userspace (from disk 
or initrd) and go through its startup process.  Xen builds a start-of-day 
environment for the dom0 guest (including setting up a boostrap pagetable 
arrangement, placing the kernel and initrd into it) and then schedules that 
guest.  The guest OS then does some initialisation stuff that's specific to 
the Xen paravirtualised environment, then it too needs to initialise its 
device drivers and start a userspace, then go through a Linux startup.

The dom0 Linux kernel will also call into Xen at various points during its 
startup in order to request operations or notify it of configuration details.

Hope that helps clarify things somewhat.

Cheers,
Mark

-- 
Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/)

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel

<Prev in Thread] Current Thread [Next in Thread>