On 06/14/2011 03:39 PM, Corey Bryant wrote:
Incremental support is fine by me, but we'll need it sooner or later.
Qemu currently opens the specified copy-on-write file, finds a backing file name in the opened file's header, opens that backing file, and repeats.
So it seems that either a backingN= would be needed or a way to map a file descriptor to the file name in the header.
I think the latter is along the lines of what was discussed here with -blockdev: http://lists.gnu.org/archive/html/qemu-devel/2011-05/msg02417.html
Repeating the syntax specified in that thread, you'd have:
-blockdev id=foo-base,path=fd:4,format=raw -blockdev id=foo,path=fd:3,format=qcow2,backing_file=foo-base
where id is the file name. This chains the backing files on the command line.
I like it. It scales as deep as we want by adding as many additional -blockdev entries prior to the -drive that uses the nested -blockdevs. -- Eric Blake eblake@redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org