Re: [Qemu-devel] Re: [PATCH 08/12] block: Catch attempt to attach multiple devices to a blockdev

[Christoph Hellwig]

On Sat, Jun 26, 2010 at 04:44:11PM +0200, Markus Armbruster wrote:
> Valid question.  I'd answer yes.  It's an easy error to make, and likely
> to end in massive file system corruption in the guest.

I suspect a modern distro in the guest will detect it as a multi-path setup.

> > Can anyone explain what the hell usb storage is actually trying to do
> > with the two drives?
> 
> It's actually a SCSI controller with a single drive on its single bus.
> 
> -device usb-storage,drive=foo creates *two* devices: usb-storage itself,
> which serves as SCSI controller, and scsi-disk for the drive.
> usb-storage copies its drive property to scsi-disk.
> 
> I don't like this.  Each -device should create just one device.

Indeed.  I'd also prefer to get rid of this.  Anthony, how hard are the
rules on backwards compatiblity for things like this?

Note that currently the usb storage emulation is extremly broken anyway,
just writing to it produces I/O errors after a short while.  This means
it can't be used very much at all.