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On 23/01/13 13:14, Daniel P. Berrange wrote:
> When booting a VM in Nova one of the parameters passed to the 'spawn'
> method in the virt driver API is 'block_device_info'. From reading
> the code I can see that this is a dict that has the following kind of
> structure:
> 
>     block_device_info = {
>             'root_device_name': "/dev/sda",
>             'swap': {
>                'device_name': "/dev/sdb",
>                'swap_size': 5,
>             }
>             'ephemerals': [
>                {'num': 0,
>                 'virtual_name': 'eph0',
>                 'device_name': "/dev/sdc",
>                 'size': 5 },
>                {'num': 1,
>                 'virtual_name': 'eph1',
>                 'device_name': "/dev/sdd",
>                 'size': 5 },
>                {'num': 2,
>                 'virtual_name': 'eph2',
>                 'device_name': "/dev/sde",
>                 'size': 5 },
>                ...
>             ],
>             'block_device_mapping': [
>                {'cinfo': {....some cinder volume data....},
>                 'mount_device': "/dev/sdf",
>                 'delete_on_termination': True },
>                {'cinfo': {....some cinder volume data....},
>                 'mount_device': "/dev/sdg",
>                 'delete_on_termination': True },
>                {'cinfo': {....some cinder volume data....},
>                 'mount_device': "/dev/sdh",
>                 'delete_on_termination': True },
>                ...
>             ],
>      }
> 
> 
> I'm doing some work in this area of the libvirt driver, so trying to
> figure out just how to test this.
> 
> I can populate the 'block_device_mapping' field with cinder volumes
> during 'nova boot' thus:
> 
>   # nova boot \
>           --image f16-x86_64-openstack-sda \
>           --key-name  mykey \
>           --flavor m1.small f16demo3 \
>           --block-device-mapping /dev/vdf=404d2b8e-a174-4d4c-9bfb-6091dc480a01:::0
> 
> Despite looking all over the code I still can't figure out how on earth
> a user can cause the 'root_device_name', 'swap' or 'ephemeral' fields in
> 'block_device_info' to be populated with anything other than None.
> 
> Can anyone enlighten me, and/or point to the documentation on this ?

Hey Daniel,

So currently root_device_name is populated form the image properties see
nova.compute.api.API._validate_and_provision_instance mostly this line:

root_device_name = block_device.properties_root_device_name(
                image.get('properties', {}))

and then nova.compute.manager._setup_block_device_mapping just gets it
from the instance. So - it can be set on the image but not passed from
the command line to boot.

swap and ephemeral are taken in a similar way, but for details see
nova.compute.api.API._populate_instance_for_bdm and
_update_image_block_device_mapping methods.

Please do correct me if I'm wrong.

I am working on enabling ephemerals and swap from the command line as
well as part of
https://blueprints.launchpad.net/nova/+spec/improve-block-device-handling targeted
for grizzly-3.

Root device is another issue - I believe it should be chosen by the
driver and not customizable, which I expect to be a point to debate
about once I manage to post the patches for review.

Hope it helps,

Cheers,

Nikola