libvirt users - Jul 2012 - Adding a second lv as vm drive: how to set the pci part

Let's say I have a vm, vm1, which has a lv as its hard drive:

    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='none'
io='native'/>
      <source file='/dev/mapper/kvmtest_vm1_rootvg'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00'
slot='0x04'
function='0x0'/>
    </disk>

I could add pickles as a second drive as follows:

    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='none'
io='native'/>
      <source file='/dev/mapper/kvmtest_pickles'/>
      <target dev='vdb' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00'
slot='0x06'
function='0x0'/>
    </disk>

but I am trying to understand the pci address entry. Must drive be on
a different slot?

On 07/10/2012 05:18 AM, Mauricio Tavares wrote:
>       Let's say I have a vm, vm1, which has a lv as its hard drive:
> 
>     <disk type='file' device='disk'>
>       <driver name='qemu' type='raw'
cache='none' io='native'/>
>       <source file='/dev/mapper/kvmtest_vm1_rootvg'/>
>       <target dev='vda' bus='virtio'/>
>       <address type='pci' domain='0x0000'
bus='0x00' slot='0x04'
> function='0x0'/>
>     </disk>
> 
> I could add pickles as a second drive as follows:
> 
>     <disk type='file' device='disk'>
>       <driver name='qemu' type='raw'
cache='none' io='native'/>
>       <source file='/dev/mapper/kvmtest_pickles'/>
>       <target dev='vdb' bus='virtio'/>
>       <address type='pci' domain='0x0000'
bus='0x00' slot='0x06'
> function='0x0'/>
>     </disk>
> 
> but I am trying to understand the pci address entry. Must drive be on
> a different slot?
The easiest way to do this is to omit the <address> line entirely when
adding the drive, and let libvirt auto-generate the next available
address on your behalf.  The <address> element exists to say what
libvirt chose, so that future migration of the domain (including if you
upgrade to newer qemu with different allocation patterns, which has
happened in the past) will still preserve the allocation pattern that
you used at the time you originally added the disk.  But unless you
specifically care where the guest sees the disk, then letting libvirt
auto-allocate is good enough.

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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