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Re: [Qemu-arm] [PATCH RFC 0/2] Versioning ARM virt machine types

From: Wei Huang
Subject: Re: [Qemu-arm] [PATCH RFC 0/2] Versioning ARM virt machine types
Date: Tue, 23 Feb 2016 12:34:49 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0

On 02/22/2016 04:14 PM, Peter Maydell wrote:
> On 22 February 2016 at 21:06, Wei Huang <address@hidden> wrote:
>> We start to see more features been added to ARM virtual machine models.
>> For the purpose of backward compatibility (e.g. migration), it is time
>> to consider versioning machine types for ARM VMs. As a beginning step, this
>> patchset defines an abstract machine type for ARM VMs. The current
>> "virt" machine is re-written based on this new machine type accordingly.
>> These patches have been verified by booting existing VMs.
>> Note that I am seeking inputs from the community by putting RFC in the
>> subject line. Please let me know your opinions. I will send out V1
>> afterwards.
> My view here is the same as it has been in the past regarding
> adding versioned machine types for 'virt': are you (in this case
> Redhat) willing to stand behind it, in the sense of taking on
> the maintenance burden of adding new machine versions, reviewing
> new code contributions for issues that require changes to make sure
> that the old versions stay looking like the old machine, testing
> that old versions look right, testing cross version migration,
> and so on?

I understand your concerns. Currently our in-house tree already carries
versioned ARM machine types, which mirror both QEMU 2.4 and QEMU 2.5.
Thus someone (including myself) from Red Hat shouldn't have any problem
of maintaining/testing it because we are already doing it downstream.
x86 and ppc have a similar situation.

> We need versioned machine types at *some* point; my intent here
> is to provide sufficient pushback to ensure that we don't give
> ourselves the maintenance headache until we truly need it...

mach-virt based products are coming soon, so versioning is just around
the corner. The advantage of introducing it upstream early is that the
upper layers in the stack have a chance to integrate, and the QEMU
downstreams don't need to diverge in how they add versioning support
themselves. This benefits not only Red Hat but also other companies.


> thanks
> -- PMM

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