Comment 3 for bug 2009849

It turns out cinder expected the backing file path to begin with /var/lib/cinder/mnt/[0-9a-f]+/ that my attempts reported here, /media/os-stores/cinder/mnt/ea003e1a1bee1aaf573aafc40cd188ff/volume-e67af022-0d5b-4253-9981-c8b34622e058 and just volume-e67af022-0d5b-4253-9981-c8b34622e058.

I found out by reading the code in the last lines of the trace (below, not reported so far), opened /usr/lib/python3.9/site-packages/cinder/volume/drivers/remotefs.py" at line 880 and edit the code so that the exception shows both what it got and the pattern its matched it against and that failed. The code modification is a gross but harmless hack so I would not merging it. However it did turn the log trace from vaguely explaining what the problem is, to exactly showing it.

File "/usr/lib/python3.9/site-packages/cinder/volume/drivers/remotefs.py", line 880, in _qemu_img_info_base
2023-03-11 12:34:25.228 315328 ERROR oslo_messaging.rpc.server raise exception.RemoteFSInvalidBackingFile(
2023-03-11 12:34:25.228 315328 ERROR oslo_messaging.rpc.server cinder.exception.RemoteFSInvalidBackingFile: File /media/os-stores/cinder/mnt/ea003e1a1bee1aaf573aafc40cd188ff/volume-e67af022-0d5b-4253-9981-c8b34622e058.3df6ef28-7f8d-45bc-a9e2-d67703c020ae has invalid backing file backing file: "/media/os-stores/cinder/mnt/ea003e1a1bee1aaf573aafc40cd188ff/volume-e67af022-0d5b-4253-9981-c8b34622e058, expected: (/var/lib/cinder/mnt/[0-9a-f]+/)?volume-e67af022-0d5b-4253-9981-c8b34622e058(.(tmp-snap-)?[0-9a-f-]+)?$".

/Nicolas