Re: [Qemu-devel] live snapshot wiki updated

[Eric Blake <eblake@redhat.com>]

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@redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org