Hi, Indeed using non-raw images should not be used over NBD. The warning however is not superfluous, since qemu does indeed probe the image format, so a malicious guest might write a qcow2 header into the raw image, thus making qemu probe a qcow2 image the next time the same configuration is used. The problem would be solved by not making qemu probe the image format over NBD, but always assume raw; but I guess this will break existing use cases, even though they were wrong from the start. Anyway, this is solved by explicitly specifying the image format to be raw, which is what the warning says.
When it comes to vvfat, we might actually put up another warning saying that vvfat is deprecated, but anyway: Here, too, the warning is suppressed by doing what the warning says. Use -drive format=raw,file.driver=vvfat,file.dir=. and the warning disappears (or driver=raw instead of format=raw, it's the same). Concluding: Doing what the warning says makes it disappear (-drive format=raw,…), which is, not coincidentally, the warning's purpose, actually. If we want to do something about this, we would have to allow protocols like NBD and vvfat be able to force the default image format used on top of them (i.e. raw). But this may break existing use cases, at least for NBD, so I'd be wary about that. Max -- 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
