Re: [Xen-devel] 2.6.37 PV on HVM issues

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Fri, Dec 03, 2010 at 04:27:20PM +0000, Alex Bligh wrote:
> Stefano,
>
>> I guess you mean the paravirtualized ones to be preferred.
>
> Ooops, yes :-)
>
>> I was referring to the device name in the disk config file option,
>> usually is "hda" in HVM config files. Some blkfront development versions
>> don't always create an xvd device, so if you manually specify xvda in
>> the disk config file you would rule that problem out (even though it
>> also depends on the behaviour toolstack and I don't remember what xend 3.3
>> would do).
>
> Would this not break booting a non-PV driver equipped kernel? In the
> general case, we don't know what guests will be booted (up to the
> customer).
>
>> But in any case upstream blkfront should always create xvd devices so I am
>> not sure how you could end up with a /dev/sda there.
>
> The /dev/sda that is there is the emulated devices. xen_watch (judging
> by the call trace) is trying to create another /dev/sda, presumably
> for the paravirtualised device (given the call path through blkfront).
>
>> If you pass a label or a UUID you cannot be sure if you end up using the
>> emulated or the paravitualized interface, unless xen supports the unplug
>> protocol.
>> Maybe the technology you mentioned before solves also this problem for
>> you.
>
> The technology is simply ensuring the modules in the kernel initialise
> in the right order. This makes UUID and label mounting prefer PV drivers.
>
> It's described here:
> http://blog.alex.org.uk/2010/05/09/linux-pv-drivers-for-xen-hvm-building-nor
> mally-within-an-arbitrary-kernel-tree/
> with patches.
>

Btw I added a link to your blog to 
http://wiki.xen.org/xenwiki/XenLinuxPVonHVMdrivers

-- Pasi



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