Re: [Qemu-devel] Deprecating old machine-types (was Re: [PATCH v4 7/8] intel_iommu: keep buggy EIM enabled in 2.7 machine type)

[Paolo Bonzini]

On 11/10/2016 10:23, Daniel P. Berrange wrote:
> On Tue, Oct 11, 2016 at 09:36:29AM +0200, Paolo Bonzini wrote:
>>
>>
>> On 10/10/2016 19:46, Eduardo Habkost wrote:
>>> I don't think we have a plan, but I would support deprecating and
>>> removing very old machine-types. The question is: how old is too
>>> old?
>>>
>>> For reference, the commits and dates when each machine-type was
>>> added are below:
>>>
>>> machine   commit    commit date  release  release date
>>> pc-0.10   e8b2a1c6  Jul 8 2009   v0.11.0  Sep 22 2009
>>> pc-0.13   95747581  Jul 22 2009  v0.12.0  Dec 19 2009
>>> pc-0.12   2cae6f5e  Jan 8 2010   v0.13.0  Oct 14 2010
>>> pc-0.13   d76fa62d  Feb 15 2010  v0.13.0  Oct 14 2010
>>> pc-0.14   b903a0f7  Nov 11 2010  v0.14.0  Feb 16 2011
>>> pc-0.15   ce01a508  Dec 18 2011  v1.1.0   Jun 1 2012
>>> pc-1.0    19857e62  Nov 7 2011   v1.0     Dec 1 2011
>>> pc-1.1    382b3a68  Feb 21 2012  v1.1.0   Jun 1 2012
>>> pc-1.2    f1dacf1c  Jun 11 2012  v1.2.0   Sep 5 2012
>>> pc-1.3    f4306941  Sep 13 2012  v1.3.0   Dec 3 2012
>>
>> Anything before pc-1.3 has issues with migration due to the introduction
>> of the memory API.  Basically, 0xf0000-0xfffff is not migrated
>> correctly, and the result is that rebooting after migration causes the
>> guest to crash.  So that could be a reasonable place to draw the line at.
> 
> That is a one-off special case - I think it would be desirable to come up
> with a general rule we can follow indefinitely, which we can apply at the
> start of each release cycle to purge old stuff.
> 
> If we wanted to pick pc-1.3 as the starting point and generalize it, we
> choose declare we'll support machine types for 4 years. Or we could do
> it in terms of number of releases - eg we'll support the last N releases
> (for 3/releases per year cadence, that'd be N == 12)

I don't know, it's already boring to create a new machine every time...
I would hate to have to remove one or more machine types every three
months.  Consider that adding new machine types will hardly introduce
bugs; what causes bugs is removing them.

Paolo