Re: [Xen-devel] A dumb question

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> because in the java source, it tests that the domain is != 0.
> 
> I modified the Java so that it accepts 0 as a domain, and what
> happened was :
> 
> error: disk number missing
> 
> followed by an Oops with a NULL pointer dereference.
> 
> I didn't dig further, because I thought that it wasn't suppose to work
> this way. But since you (well, Ian) implies that it shall work, I'll
> try to get into the kernel source to see what's going on.
> 
> Any idea welcomed, however :)

Hmm sorry. I'm afraid we tend to use either physical partitions or
NFS roots, so the virtual disk stuff doesn't get exercised much.
It used to work...

One trick that may help to debug things is that you can attach a
physical partition as a block device.

i.e. suppose you had an empty partition hda3. You could use
'physical grant' to enable another domain to access it (dom0 gets
access by default). However, you could also attach it to a domain
as a virtual block device i.e.

 xenctl vbd create -phda3 -v0 -w -n0 

You could then access the partition as /dev/xvda
(in this instance, you probably wouldn't want to put a partition
table on the 'virtual' disk).

Arrgh. I've just tried this and get the error message you
reported: "Expected -n<domain_id>"

I've blown away the three obvious lines in ParseVbdCreate.java
and retried it, and it seems to work. I didn't get an Oops:

iap10 > xenctl vbd create -p sda14 -v1 -n0
warning: state file not found [/var/lib/xen/vdstate.xml]
Created virtual block device 1 for domain 0
XML.dump_state error [/var/lib/xen/vdstate.xml]
java.io.FileNotFoundException: /var/lib/xen/vdstate.xml (No such file or 
directory)
iap10 > mount /dev/xvdb /mnt
iap10 > ls /mnt
anfs/  dev/   home-old/  lib/         misc/  proc/  tmp/
bin/   etc/   homes/     local/       mnt/   root/  usr/
boot/  home@  initrd/    lost+found/  opt/   sbin/  var/
iap10 > 

[ignore the warnings about /var/lib/xen/vdstate.xml -- I haven't
created any virtual disks]

I haven't been able to try the "virtual disk" stuff as I haven't a
spare partition on my test machine. I'll make one free if you're
still having problems ;-)

Best,
Ian


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