01.04.2015 15:34, Kevin Wolf wrote: [] > Overriding the backing file should work like this: > > -drive file=...,backing.file.filename=/dev/fdset/2
Oh-ok, this works. Sort of. Because after performing commit (is there a difference between commit hmp command and block-commit qmp command? I used the former so far), the new backing file name is recorded to the qcow2 file header, and now, qemu-img can't operate on this file anymore, telling me it can't access backing file due to bad file descriptor. So in order to finally commit the file I used qemu-system again, running it like that specifying backing file, but with -S option, and issued `commit' command again. I noticed that I can't specify backing file for qemu-img commit. But overall, I think qemu-system should not modify backing file name in this case. When performing commit, does qemu mark the areas in the overlay file as free after writing contents to the backing file, or will these areas be written again by a subsequent commit? Somehow it smells like each next commit writes more and more data and completes in more and more time. Thanks, /mjt