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Re: [Xen-users] Trouble booting domU over NFS

To: "XEN Mailing List" <xen-users@xxxxxxxxxxxxxxxxxxx>, "Nick Couchman" <Nick.Couchman@xxxxxxxxx>, "Steve Thompson" <smt@xxxxxxxxxxxx>
Subject: Re: [Xen-users] Trouble booting domU over NFS
From: "Nick Couchman" <Nick.Couchman@xxxxxxxxx>
Date: Tue, 14 Sep 2010 13:27:56 -0600
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> 
> Thanks for the response, Steve.  I guess I assumed that, since the openSuSE 
> mkinitrd supported the addition of NFS features, this would support root over 
> NFS.  Perhaps this is not the case and the NFS support in initrd is intended 
> for something else.  In any case, I'm compiling a new kernel with the options 
> similar to what you specified above and I'll see if that works.  It'll have 
> the side benefit of being a much leaner kernel, and of not requiring an 
> initrd, but I much prefer to stick with the vendor-provided, stock kernel 
> when 
> possible.  Anyway, I'll see where this gets me.
> 
> -Nick
> 

Tracked it down to two silly problems:
- First, my DHCP server had a root server/path option specified, which, 
apparently overwrites anything you pass to Linux on the command line.  I'm 
assuming this is done intentionally and is sort of a security feature as it 
prevents folks from messing around with the root paths passed by DHCP and 
pointing the system off on some other path, but it did throw me a little.  I 
ended up doing a tcpdump and looking at the traffic, and saw the system looking 
for the wrong DHCP server.  I removed that option from the DHCP server and, 
what do you know, it started mounting the correct root FS!
- The second problem was the one with the CONFIG_ROOT_NFS not being compiled 
into the kernel.  So, I compiled a custom kernel with CONFIG_ROOT_NFS enabled 
and removed a bunch of other stuff that I'll never use in a xen domU (pretty 
much all the device drivers :-).
- The final issue was that, apparently I needed to explicitly pass the 
"console=xvc0" option in the extra parameter of the domU config.  I still 
haven't figured out exactly why this was necessary, but it was, and it works 
fine, now.

On to the next challenge - using AUFS2 so that I can have a common, read-only 
NFS base for all the domUs, with individual NFS shares for the configuration 
files, etc., for the domUs.  If anyone has hints on this or would like to point 
me in the direction of some documentation from someone who's already done it, 
I'd certainly appreciate it!  I took the opportunity recompiling the kernel to 
patch it with AUFS2 and compile it in, so that piece is taken care of - just 
have to figure out all the magic initrd stuff that needs to happen to make it 
work properly.

-Nick



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