How do I force Xen to present physical devices to multiple guests simultaneously in read-write mode? (Read on before answering!)

I've got about 20 device files (multipath device files corresponding to SAN luns) on my physical host that I want presented read-write to three different guest OSes. By default, Xen tries to prevent me from doing this, which in many cases is understandable.

But what I want to do is legitimate. It's an Oracle environment, and any entity that's going to be writing to the devices in the guest OSes is cluster-aware, and will manage all of the reads/writes internally. This isn't going to be ext3. It will be a lot of OCFS2 and Oracle ASM.

Thanks in advance.

Ah - looks like I found it. I used a '!' after the w in the 'phy' entry in the Xen config, and this seems to do what I need.

Any kinks I need to be aware of using this?