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Date: Thu, 28 Aug 2014 17:39:47 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2] block: Introduce "null" driver
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To: Markus Armbruster <armbru@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, benoit.canet@irqsave.net, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On Thu, 08/28 10:22, Markus Armbruster wrote:
> Fam Zheng <famz@redhat.com> writes:
> 
> > This is an analogue to Linux null_blk. It can be used for testing block
> > device emulation and general block layer functionalities such as
> > coroutines and throttling, where disk IO is not necessary or wanted.
> >
> > Use null:// for AIO version, and null-co:// for coroutine version.
> >
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> >
> > ---
> > V2: Don't #ifdef code, add two drivers. (Benoit)
> >     Add to QAPI BlockdevOptions. (Eric)
> >     Add "file.size" option to override backend size. (What is a better
> >     way to associate /dev/vd{a,b,c} with command line devices, if sizes
> >     are the same?)
> 
> Is this a request for advice?  If yes, please explain the problem in
> more detail, because I'm too dense to get it :)
> 

Yes :)

I have more than one virtio-blk:

-drive file=/dev/ram0,id=d0,if=none -device virtio-blk-pci,drive=d0,x-datap-plane=on \
-drive file=/dev/ram1,id=d0,if=none -device virtio-blk-pci,drive=d1

Then I get /dev/vda and /dev/vdb in guest. They are in the same size.

The question is how do I tell which is /dev/ram0 and which is /dev/ram1,
without bothering peaking PCI addr, etc.?

Fam