On Fri, Dec 08, 2017 at 10:59:22AM +1100, Dave Chinner wrote: > > 3. if multi nested looped fs is important (not really) then loop/nbd will > > need to know if its file is on a looped fs and propagate nesting level > > to ext4 > > This functionality is definitely used and needs to be supported by > the annotations. FWIW, in addition to loop, there's md. So should loop need to know if its backing file lives on a filesystem that does, for example, have an extrnal journal sitting on RAID1 with one of the components hosted in a file on some other fs, brought into the array via another loop device? Oh, and to make life even more fun, backing file can be flipped under configured /dev/loop. IOW, those nesting depths are not static at all.
