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Re: [Xen-devel] Almost working iSCSI booting, need advice

To: Stefan de Konink <skinkie@xxxxxxxxx>
Subject: Re: [Xen-devel] Almost working iSCSI booting, need advice
From: jpranevich@xxxxxxxxxxx
Date: Fri, 22 Aug 2008 21:54:01 -0400 (EDT)
Cc: Stephan Seitz <s.seitz@xxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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----- "Stefan de Konink" <skinkie@xxxxxxxxx> wrote:

> I guess here is where the problem is... I never used pygrub before it.
> So if you are hacking in PyGrub you might be in the right place ;)

Can you tell me what bootloader you are using and whether you have any patches 
on top of stock Xen, particularly in XendDomainInfo.py or XendBootloader.py? 
I'll try and reproduce your setup and trace the code path for what you are 
using. There are some weird conditional statements in the Python for what 
bootloader you are using (especially in the SuSE patches), and there could be 
something in there. 

As far as I can tell _configureBootloader(), where my changes are, sets up the 
environment for the bootloader. It could be that the hotplug code happens there 
or at some other place. I've had significant difficulties understanding it, 
which is why I was hoping to get a response from an "expert" on the list in 
this area. I understand how it works once /etc/xen/scripts/block is executed, 
but not all the assumptions leading up to that point.

> You ask smart questions... but I don't know 'how' PyGrub does this.
> And 
> actually I have no clue were in the actual booting process PyGrub
> steps in.

Something like:


I'll look deeper into PyGrub, the new bootloader, and whatever you are using on 
Monday and try and figure out where my issue is from there.

(As an aside, Xen really does seem intent on thinking that you need a real 
block device to boot from in a few other areas. I was playing around and was 
able to get RedHat AS 5.2's newly-added root-on-iSCSI support working under Xen 
without any code modifications using the SuSE domUloader and RedHat's initrd 
and kernel, but I still had to specify a block device, even though it's ignored 
by the initrd which has its own mini-open-iscsi built in and mounts root from 
that. The RedHat support has too many limitations to be practical for Xen just 
yet, but it's an interesting different approach. Still, having Xen manage the 
iSCSI connections appears to be the best way.)


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