Re: qemu-kvm.git now live

[Avi Kivity <avi@redhat.com>]

Jan Kiszka wrote:
>> If migration disables dirty memory logging, it must keep the vga logging
>> enabled, and vice versa.
>>     
>
> So we need some notifier callbacks on slot changes so that all users can
> re-enable dirty logging after the update as required. 

Simpler to do reference counting.  When a user enables logging for a 
memory range, the refcount for all slots containing that range gets 
bumped.  When a user enables logging for all of memory, a global 
refcount is bumped.  For a given slot, dirty logging is enabled if 
either the slot logging refcount or the global logging refcount is nonzero.

That's sort of what's implemented in qemu-kvm.git.  In qemu.git vga 
logging does not get disabled, which is really broken.  It prevents 
optimizations like disabling logging when the screen is not displayed to 
a human.

> Where/how does the
> migration code disable dirty logging?
>   

Should be phase 3 of ram_save_live().

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.