Getting WinXP (or Win 7, Server etc) to see all cores as a KVM guest

I'd installed a Win XP Pro x86_64 guest on a Fedora 13 x86_64 KVM host. The host had 8 hyperthreaded CPUs (16 virtual cores in total). I had assigned all 16 vcpus to the WinXP guest, but it only showed 2 in the task manager, though in the device manager, it showed 16. The problem had to do with licensing: XP Pro is limited to 2 physical CPUs (even though it can see 16 cpus in the device manager). It can support (at least) 4 cores per cpu however. So the solution is to specify this in the config, which I found (via googling) can be done by modifying the xml defining the guest. To find the layout of the host:

virsh capabilities | grep topology

<topology sockets='2' cores='4' threads='2'/>

Using 'virsh edit <domain>', find where the vcpus are set:

<vcpu>16</vcpu>

Then add the following below:


  <cpu>
    <topology sockets='2' cores='4' threads='2'/>
  </cpu>

Save it, and restart the guest. It now sees all vcpus.

I notice that from looking at the xml, libvirt reorders it slightly:


  <vcpu>16</vcpu>
  <os>
    <type arch='x86_64' machine='pc-0.13'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <cpu>
    <topology sockets='2' cores='4' threads='2'/>
  </cpu>

editfiles cfengine v2

I had the task of disabling swap on a class of machines managed by cfengine2

The swap entry could have started with 'UUID=', or possibly '/dev/sda3'


One way of doing it:


editfiles:
    { /etc/fstab

            CommentLinesMatching ".*swap(\s+)swap(\s+).*"
     }

another, more complicated way:


editfiles:
    { /etc/fstab
        ReplaceAll "swap(\s+)swap(\s+)defaults(\s+)0(\s+)0$" With "swap                    swap    noauto,defaults        0 0"
}

Normally, with editfiles, you must match the whole line (hence the .* at the beginning and end of the first way using 'CommentLines'), but when matching a quoted regex (as with 'ReplaceAll'), you can just match (and replace) that part of the line

Unpack and edit initramfs (for blacklisting modules, but can be used for other reasons)

I did this originally to blacklist the loading a kernel module, which may have been loaded by initramfs (adding rdblacklist to the kernel command line didn't work). However, the module still got loaded and what I should have done in the first instance was check modules.dep, as it was a dependency for another module that I wanted anyway. You also must make sure any other processes in init don't cause it to get loaded. Anyway, it was a useful exercise in how to modify initramfs!

How to unpack and modify a initramfs image

(tested with fedora 13)

Make a directory to unpack it in
Make a backup of the original initramfs image
cd to your unpack dir and unpack with: 'gzip -dc initramfs-2.6.34.9-69.fc13.x86_64.img | cpio -id'

The 'i' flag is for taking input, and the 'd' makes dirs

Modify the files as required

Recreate the image (I like to do it in 2 separate steps cos I'm superstitous):


find . | cpio -H newc -o > /some/dir/initramfs-2.6.34.9-69.fc13.x86_64.cpio

'-H' - format
newc - is the newc format type

'-o' - output

cat /tmp/initramfs-2.6.34.9-69.fc13.x86_64.cpio | gzip -9 > /tmp/initramfs-2.6.34.9-69.fc13.x86_64.img

Maximum compression is selected as that is what it is used in the original

Then copy it back

I haven't yet tried dracut