Re: [Libguestfs] Extracting files from OVA is bad

Hi, just to keep this thread alive, here are few comments on the progress. (Mostly for those not following QEMU mailing lists.) On Fri, 9 Sep 2016 15:18:02 +0300 Roman Kagan <rkagan(a)virtuozzo.com&gt; wrote: Using the loopback device would be the easiest solution in the sense that it wouldn't require code changes outside virt-v2v. But, there's a big issue: it requires root privileges. That's why I cast this idea away from the beginning and decided to use that only as the last resort. Other suggestion was to use qemu-nbd because it already has --offset argument to set where the disk starts. It turned out that: a) The code for --offset is buggy and clients may attempt to read data outside the backing file, because qemu-nbd reports wrong size of the disk. Such request will inevitably fail. b) We also need to be able to specify the size of the disk. It cannot be left undefined and limited only by the length of underlying file. Security reasons aside, there are also some practical reasons. E.g. it turned out that VMDK format stores some footer at the end of the disk. If the size of the disk is not set properly the VMDK driver fails to find the footer and regards the disk as invalid. I fixed the issues and sent patches to QEMU [1][2]. Quickly somebody commented [3] that doing this in qemu-nbd is not the right idea and it should be done in the raw driver... ... that is something what Roman suggested from the start. It'll be more complicated than fixing qemu-nbd, but I gave it a shot. I have sent the first version [4] of that to QEMU. I would expect it going in right away, there's still some work to be done. That being said, I also have POC ready (attached) for virt-v2v. It's rather dirty as it contains some 'tar' invocations to get the necessary information from the archive. There are some OCAML modules for working with tar archives, but I didn't try any yet. Good thing is that QEMU people are not against putting the size & offset parameters into raw driver. Still it may turn out to be a task too hard. In that case, as a fallback, we can still use the NBD approach. We don't have to use qemu-nbd. We could also try to submit code for size & offset into the nbd-server in NBD tools (the defacto reference implementation). But that's something I didn't pursue yet. Tomas [1] https://lists.nongnu.org/archive/html/qemu-devel/2016-09/msg04554.html [2] https://lists.nongnu.org/archive/html/qemu-devel/2016-09/msg04556.html [3] https://lists.nongnu.org/archive/html/qemu-devel/2016-09/msg04578.html [4] https://lists.nongnu.org/archive/html/qemu-block/2016-10/msg00008.html -- Tomáš Golembiovský <tgolembi(a)redhat.com&gt;