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

Nicolas Sebrecht nsebrecht at piing.fr
Wed Jul 20 10:15:02 UTC 2011

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.

> 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.

Nicolas Sebrecht

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