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Re: [libvirt] [Qemu-devel] live snapshot wiki updated



On Wed, Jul 20, 2011 at 12:15:02PM +0200, Nicolas Sebrecht wrote:
> The 20/07/11, Daniel P. Berrange wrote:
> 
> > To make the decision whether the filename from QEMU is valid, we have
> > to parse the master image header data to see if the filename actually
> > matches the backing file required by the image assigned to the guest.
> 
> Actually, libvirt should not have to worry if the filename provided by
> QEMU is valid. I think it should trust QEMU. If QEMU doesn't provide
> information others can trust; it should be fixed at QEMU side.

The security goal of libvirt is to protect the host from a compromised
QEMU, therefore QEMU is, by definition, untrusted.

> > We're not fighting over the internals of metadata. We just need to know
> > ahead of launching QEMU, what backing files an image has & what format
> > they are in. We do that by reading at the metadata headers of the disk
> > images. We never attempt to write to the disk images. Either someone
> > provides a library todo that, or we write the probing code for each
> > file format in libvirt. Currently we have the latter.
> 
> This is what I would call "fighting with QEMU internals". How do you
> prevent from concurrency access and modifications? Ideally speacking
> libvirt should be able to co-exist with foreign implementations, all
> requesting QEMU.

QEMU is *not* yet running at the time libvirt reads the file metadata.

Daniel
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