Re: [Libguestfs] [nbdkit PATCH 0/3] Fix data integrity in vddk plugin

On Tue, Apr 30, 2019 at 01:03:28PM +0100, Richard W.M. Jones wrote: I actually thought of this from a more generic point of view, not just my use case. What VDDK exposes is really not something that is really unusable from any point of view. Be it qemu-img, any other client or users. The resulting data makes single-link=true completely unusable. Well, unless the extent granularity on the source block device and the file format is exactly equal to the CHUNK_MIN_SIZE, but nobody can ever guarantee that. I also thought of a way how to have nbdkit handle "backing chains" (it would basically have a list of plug-ins and the first one that has data available would be used), but that seemed too much of a hammer. It could also be handled by a specialized filter where the filter would provide extents from single-link and plugin would do the rest. But, honestly, that sounds worse to me than what I posted in the first patch. Maybe the filter could just take a plugin as a parameter, e.g. "intercept extents and use this plugin for those calls", or even generalize it to a specified list of APIs that it should intercept. Both above approaches would need the user to explicitly specify what needs to be done and they would really need to know how all the details fit together just to be able to use it, even though there is a possible solve-all solution (without which the single-link does not really has a standalone use case).