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

Eric Blake eblake at redhat.com
Wed Jul 20 13:46:58 UTC 2011

On 07/20/2011 07:25 AM, Jes Sorensen wrote:
>> I think if libvirt wants qemu to use an fd instead of a file name, it
>> shouldn't pass a file name but an fd in the first place. Which means
>> that the two that we need are support for an fd: protocol (patches on
>> the list, need review), and a way for libvirt to override the backing
>> file of an image.
> The problem is that QEMU will find backing file file names inside the
> images which it will be unable to open. How do you suggest we get around
> that?

We've already told you - qemu must have a way to be passed fds which are 
associated with names, and when a file refers to another backing file by 
name, then qemu falls back on its fd/name mapping to use the 
already-passed fd instead.  Which implies that someone else, either 
libvirt or a qemu-maintained libblockformat.so, needs to have a stable 
interface for parsing the backing file name out of an arbitrary qcow2 
file, and that this interface must work no matter how many other 
extensions are added to qcow2.

Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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