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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2013-01-21 at 10:19 +0000, Roger Pau Monne wrote:
> 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.

OK, I think I follow. Presumably a similar hack would be needed to make
the local_attach interface do something useful here too.

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

Fair enough.

In the meantime I suppose James could work around this by logging into
rdb manually (or in a script) before starting the domain and
specifying /dev/rdbN in the guest config?

Ian.


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