Re: [Xen-users] RFH: loopback & blktap(2) and CDROM

[Philipp Hahn <hahn@xxxxxxxxxxxxx>]

Hello,

On Friday 09 November 2012 16:49:32 Ian Campbell wrote:
> > 4. I read somewhere that "mixing loobback with tapdisk is a bad idea", but 
> > I 
> > can't find that again, so I'm wondering if that (wrong) claim got somehow 
> > stuck in my memory. I can only imagin two scenarios

I found it again in <http://wiki.xenproject.org/wiki/Blktap2#Usage>
> Notice: In Xen 4.0.0/4.0.1 don't mix file and tap simultaneously, in this 
> case domU unable to see any disk device. May be bug or feature!

I hope that bug is fixed since 4.0.1, because the descriptions sounds a little 
bit like my other finding:

> > 5. While experimenting with a Linux domU I noticed that the boot process
> > sometimes gets stuck when I declare one disk as "hda" and a second one
> > as "xvda". The 2.6.32 kernel detects a clash in /sys/block naming and I'm
> > stuck in the "XENBUS: Waiting for devices to initialise: 295s..." count
> > down. Is this because hda and xvda overlap because of the PVonHVM case
> > (ide-block-major has 64 minors per device for partitions, while
> > scsi-block-major and xen-block-major only have 16 minors per device
> 
> When you ask for hda you actually get hda+xvda in order to allow for the
> switchover described above. So you've actually asked for 2 xvda's --
> don't do that ;-)

Sincerely
Philipp

PS: The link to the blktap2 README on the Wiki-page is broken
-- 
Philipp Hahn           Open Source Software Engineer      hahn@xxxxxxxxxxxxx
Univention GmbH        be open.                       fon: +49 421 22 232- 0
Mary-Somerville-Str.1  D-28359 Bremen                 fax: +49 421 22 232-99
                                                   http://www.univention.de/

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