[Qemu-devel] Re: [PATCH 03/26] Remove SaveVM v2 support

[Juan Quintela <quintela@redhat.com>]

Stefano Stabellini <stefano.stabellini@eu.citrix.com> wrote:
> On Fri, 11 Sep 2009, Juan Quintela wrote:
>> I think we can't call that a regression:
>> 
>> Old in the past SaveVM State v2 is created.
>> 
>> Everything works for a while.
>> 
>> At some later point SaveVM State v3 is created.
>> 
>> Things continue to work fo a while.
>> 
>> After this while (In April of this year ram support for V2 got broken, when I fixed
>> it, I found that VGA got garbled and ide didn't work either).
>> 
>> Things didn't work for at least 5 months, I haven't seen a complaint.
>> 
>> Removing something that hasn't work during 5 months and nobody
>> complained is supposed to be a regression?
>> 
>> Now: We have v2 support on tree, that is not working, haven't worked for
>> a long time, and there is not a chance to load an image from the old
>> past.  What is better?  Remove the old non working code.  Or spend time
>> debugging why it stopped working and fixing it?  Notice that it is also
>> important that nobody complained that they were unable to load the old images.
>> 
>
> No one complained because the people affected by this issue probably
> don't follow qemu development so closely to have realized that their old
> images won't work anymore.
> I do believe that fixing v2 compatibility is important for a large
> number of qemu users (including kvm and xen).

About this, nobody is wanting to remove useful features.  I was removing
things that didn't work.  The best plan of action if you want v2 support
on tree is to fix it.  Do what I did:

This commit introduces SaveVM v3
commit 9366f4186025e1d8fc3bebd41fb714521c170b6f
Author: aliguori <aliguori@c046a42c-6fe2-441c-8c8c-71466251a162>
Date:   Mon Oct 6 14:53:52 2008 +0000

    Introduce v3 of savevm protocol

I checkout previous commit, savevm one machine. Go to the present and
try to load it -> RAM don't work.

Search what commit broke it:

commit 94a6b54fd6d2d3321066cb4db7abeeb417af9365
Author: pbrook <pbrook@c046a42c-6fe2-441c-8c8c-71466251a162>
Date:   Sat Apr 11 17:15:54 2009 +0000

    Implement dynamic guest ram allocation.

Went to the previous one, to see if this was the only broken thing.
And found that ide and vga was broken at that point.

I stopped searching there.
You get that image to load, and I try not to break it with VMState
changes.  Can you (or anybody else) got v2 to life?  If it is working,
and you can use it, I don't want to break its support.  But if it has
been broken for ages and nobody steps it to fix it -> removing is only
useful thing that I can think of doing.

> That said, I don't want to fight over this more than necessary, so as
> long as you keep the per device loading functions in C we can maintain
> v2 compatibility downstream if upstream is not interested.

Instead of complaining, we can start doing things productively.
Can you do a list of the older (device, version) that you are interested
in?  If we have such a list, we can see how feasible it is maintaing
support for them.

Later, Juan.