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Date: Tue, 12 Aug 2008 13:42:01 +0200
From: Kevin Wolf <kwolf@suse.de>
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Subject: Re: [Qemu-devel] PATCH: v3 Allow control over drive file open mode
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To: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: qemu-devel@nongnu.org

Ian Jackson schrieb:
>> qemu-system-x86_64 -drive file=foo.img -drive file=boo.img,read-only=on
>>
>> Down the road, you do a savevm.  savevm has to create a checkpoint in 
>> all disk images.  The checkpoint will be empty in boo.img but it still 
>> needs to create one.
> 
> Perhaps I don't understand clearly enough how you imagine this
> scenario.  Surely when the snapshot is resumed it is sufficient for
> the file boo.img to be identical ?
> 
> What are these checkpoints ?  Are they currently written by anything ?
> 
> I've tried to look for the code you would be referring to but I can't
> seem to find it.  qemu_savevm_state just calls all the things recorded
> with register_savevm and I can't seem to find anything that would do
> anything to block drivers. 

This code is in do_savevm (in vl.c). Look for /* create the snapshots */

Kevin