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Re: [Xen-devel] pygrub/hvm boot with alternate script= for block devices

On 21/01/13 11:01, Ian Campbell wrote:
> On Mon, 2013-01-21 at 09:56 +0000, Roger Pau Monnà wrote:
>> On 19/01/13 16:46, James Dingwall wrote:
>>> Hi,
>>> I am doing some experimentation with xen and Ceph and have a problem
>>> booting my guest when my disk = [] uses an alternate block script.
>>> Installation from a .iso was ok since the boot device was a file but 
>>> now
>>> trying to boot from the rbd neither the hvmbuilder or pygrub can start
>>> as they treat the first value after target= as the /dev node to try and
>>> use.
>> Yes, this is known problem which I'm trying to solve with this series:
>> http://lists.xen.org/archives/html/xen-devel/2012-12/msg01753.html
>>> My disk parameter looks like:
>>> disk = [ 'format=raw, script=block-rbd, vdev=xvda, access=w,
>>> target=image=ubuntu-test' ]
>>> In the pygrub log:
>>> OSError: [Errno 2] No such file or directory: 'image=ubuntu-test'
>>> and there is a similar error trying an HVM boot.
>>> My block-rbd script parses the value passed after target= to
>>> dynamically rbd map the image and then call the write_dev function from
>>> block-common.sh to save the corresponding /dev name in xenstore.
>>> According to the logging that I have in my block-rbd script this isn't
>>> even called before pygrub is executed.
>> The only solution right now will be to use PV guests and boot directly
>> with the kernel (no pygrub)
> Does commenting out the stat & check in the short term allow things to
> work well enough for James' purposes?

Current hotplug scripts don't have any need to write the dev in
xenstore, they only need to write the device major:minor in the
physical-device xenstore backend entry. The only way to solve this (with
current hotplug scripts) will be to call libxl_device_disk_add earlier
on (before pygrub), fetch "physical-device" from xenstore and translate
that back into the physical device it points to, and overwrite pdev_path
in libxl_device_disk struct with this value.

I would rather wait for the new interface to be finished rather than
adding this "hack" to libxl.

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