> I could actually see the use of non-raw over NBD. We support nested > protocols (where you can use qcow2->qcow2->file), that is, where a file > contains a qcow2 file whose contents are themselves a qcow2 image. > (Perhaps useful in nested guests, where the outer qcow2 layer serves a > disk to an L0 guest, which in turn uses the inner layer to present a > disk to an L1 guest). In such a case, opening just one layer of qcow2 > for service over NBD will expose the inner qcow2 image, and connecting > qemu as an NBD client with format=raw will directly manipulate the qcow2 > data seen by the L0 guest, while connecting as an NBD client with > format=qcow2 will see the raw data seen by the L1 guest.
Seems like an academic exercise, really. But if this use case is practical, I believe three levels of wrapping is just as useful, and the only way to work with that one is to run two or three instances of qemu- nbd. With more layers, the set-up quickly becomes tangled and unmanageable. And I still doubt anyone would actually want to create a set-up like this. It seems incredibly wasteful (but then, so is virtualisation in general, so maybe that isn't an issue) and doesn't seem to accomplish anything that couldn't be done with just one layer of wrapping. -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1474263 Title: "Image format was not specified" warning should be suppressed for the vvfat (and probably nbd) driver Status in QEMU: New Bug description: Running qemu -drive file.driver=vvfat,file.dir=. displays WARNING: Image format was not specified for 'json:{"dir": ".", "driver": "vvfat"}' and probing guessed raw. Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted. Specify the 'raw' format explicitly to remove the restrictions. However, since "images" provided by the vvfat driver are always raw (and the first sector isn't writeable in any case), this warning is superfluous and should not be displayed. A similar warning is displayed for NBD devices; I suspect it should be also disabled for similar reasons, but I'm not sure if serving non-raw images is actually a violation of the protocol. qemu-nbd translates them to raw images, for what it's worth, even if it may be suppressed with -f raw. Noticed on 2.3.0; the code that causes this behaviour is still apparently present in today's git master (f3a1b5068cea303a55e2a21a97e66d057eaae638). Speaking of versions: you may want to update the copyright notice that qemu -version displays. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1474263/+subscriptions
