Re: [Qemu-devel] Re: [PATCH] block: Enable fall-back to read-only for backing file

[Christoph Hellwig]

On Mon, Feb 01, 2010 at 10:25:52AM +0100, Alexander Graf wrote:
> We don't know beforehand if a user will use the commit comnand during  
> tje runtime of the vm.
> 
> IMHO it'd be best to always open backing files read only and try to  
> open them for write access on the commit command. That command can  
> then fail gaciously.

That's another option.  Basically this means opening another
BlockDriverState for the backing device that is writeable inside
bdrv_commit().