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

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.