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

[Jes Sorensen]

On 07/20/11 12:28, Daniel P. Berrange wrote:
> On Wed, Jul 20, 2011 at 12:15:02PM +0200, Nicolas Sebrecht wrote:
>> 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.

Well that part goes both ways. By applying this model you are going to
make it a hard requirement for libvirt to be upgraded with QEMU even for
smaller updates.

>>> 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.

Of course it is: hotplug

Jes