Re: [Qemu-devel] [PATCH v7 0/3] hw/arm: Add 'virt' platform

[Peter Maydell]

On 15 October 2013 16:14, Tom Sutcliffe <address@hidden> wrote:
>
> On 15 Oct 2013, at 16:00, Peter Maydell <address@hidden> wrote:
>
>> On 15 October 2013 15:58, Tom Sutcliffe <address@hidden> wrote:
>>> Thumbs up from me testing on Arndale. My only issue is that virt and 
>>> vexpress-a15 add virtio-mmio devices in the opposite order to each other, 
>>> for the same set of -device command line arguments. It would avoid future 
>>> headaches if we could have these behave the same. My preference would be 
>>> for the virt behaviour, as the -device order matches the order in which the 
>>> guest Linux kernel adds them to /dev (for virtio-blk-devices at least).
>>
>> Oh yes, I'd forgotten you mentioned that. Did anybody ever
>> track down *why* the kernel is reading the device tree
>> backwards?
>
> Not me :)

So apparently the kernel makes no guarantees at all about what
order it might process the virtio-mmio transports in. This
means that users mustn't rely on /dev/vda and /dev/vdb
corresponding to particular virtio-blk devices on QEMU's
command line -- you need to use UUIDs or something similar
instead.

I think this sucks, but that's the kernel for you.

I'll probably change QEMU anyway, just because if there's
no guarantee we might as well make qemu code do a simple
forwards loop rather than a backwards one.

-- PMM