QEMU/KVM Panic on USB Mount

Sean Bruno seanbru at yahoo-inc.com
Fri Jul 9 23:59:44 UTC 2010

On Fri, 2010-07-09 at 17:16 -0500, Hans Petter Selasky wrote:
> On Friday 09 July 2010 19:12:59 Sean Bruno wrote:
> > In order to come up with the most convoluted problem possible, I present
> > to you screen shots of a panic from a FreeBSD VM running in QEMU
> > emulation under RedHat's KVM infrastructure.
> > 
> > I presented a perfectly functional USB partition from my host machine to
> > the VM.  Then I attempted to mount the partition from FreeBSD and it
> > generated the panics located here:
> > 
> > http://people.freebsd.org/~sbruno/usb_panic1.png
> > http://people.freebsd.org/~sbruno/usb_panic2.png
> > 
> > This is 100% reproducible.  But not an emergency or anything.
> It might be that there is a conflict that both the VM and the OS is accessing 
> / loading drivers on the same USB device. The panic seems not directly related 
> to USB.
> --HPS

Could be.  I've played with the way KVM/QEMU emulates the USB drive.  It
has four "types" it can present, IDE, SCSI, USB or VirtIO.  SCSI seems
to work fine on an emulated sym(4) target.

The VM itself is not booting off of the USB drive, it is booting off of
its own drive.  I'm attaching the USB disk as a secondary drive, so
there's no "drivers" being loaded off of it at boot time.  Is this what
you were hinting at?


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