Re: Xen and LVM backed domu's

[Brian <brian%planetunix.net@localhost>]

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Sam Fourman Jr. wrote:
> 
> I am confused a bit, doesn't  this fix these issues?
> 
> src/sys/arch/xen/xen/xbdback_xenbus.c v 1.31
> Finaly fix problems with using WEDGE like devices as xen backend devices.
> 
> or is this issue specific to HVM's
> 
> Sam Fourman Jr.
> 

No it does not, as this appears to be HVM specific.  I noticed the same
problem Hugo reported recently and I have spent a small amount of time
trouble shooting this.

I usually use the character devices for my partition-backed domU's, like
/dev/rraid0j; however, with the dm driver (and phy:/dev/mapper/rv0-lv0)
I am getting an EBUSY error on VOP_OPEN in xbdback_xenbus.c.  The qemu
BIOS then reports 0MB as Hugo described.

Any combination of /dev/mapper/v0-lv0 or /dev/mapper/rv0-lv0 produces
different errors from xbdback_xenbus.c while reporting 0MB in the qemu BIOS.

If I specify /dev/mapper/v0-saturn, I get this in my dmesg:
xbd backend: attach device v0-saturn (size 62914560) for domain 10

But qemu BIOS still reports 0MB for the drive.

If I specify /dev/mapper/rv0-saturn, I get this instead:
xbdback backend/vbd/11/832: unknown device 0xc202

With a disk entry like: 'phy:/dev/mapper/rv0-saturn,hdb,w'
Regardless of what I replace hdb with, the 0xc202 device number just
changes but still fails.

I have noticed that on one of my other HVM domU's which uses physical
drives (/dev/rwd2d) that an unknown device error from xbdback_xenbus.c
does not affect qemu's detection of the disk size.

When specifying the character device rv0-saturn, I do not get any
messages in my /var/log/xen/qemu-dm-saturn.log; however, when I specify
the block device v0-saturn, I get this:

qemu: could not open vbd '/local/domain/10/device/vbd/832/phantom_vbd'
or hard disk image '/dev/mapper/v0-saturn' (drv 'phy' format 'raw')

I will continue to work on figuring out why this is happening as I know
Adam is busy.  I do not have any other HVM-capable machines here for the
time being so my progress is slow as the machine I was debugging with is
used for production.

Sincerely,
Brian Brombacher
PlanetUnix Networks
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