On 10/16/2012 11:51 AM, Corey Bryant wrote: > This series adds command line file descriptor passing support > via a new -add-fd option. This is a follow-on to the existing > QMP fd passing support provided in the following patch series: > comments.gmane.org/gmane.comp.emulators.qemu/165463 > > The new -add-fd option is designed to mirror the add-fd QMP > option as much as possible. Before this can still be useful in libvirt, we need a way to pass in fds for all of a backing chain, and not just the top-level. And you can't argue that libvirt should be temporarily rewriting qcow2 metadata to stick in names such as /dev/fdset/1 into the metadata. Consider the case of: /- guest1.img base.img <- snap1.img < \- guest2.img snap1.img is supposed to be read-only, and there's no guarantee that /dev/fdset/1 will be available for both guest1 and guest2 to rewrite the header. Thus, I argue that snap1.img must encode the name base.img in its metadata, but that we must also have a way to tell qemu to open /dev/fdset/1 instead of trying open(base.img) in order to get the open fd for base.img.

But even though we are still not at a point where the overall feature is useful, I can at least review these patches for getting us incrementally closer to our goal.