On 4/29/21 4:59 AM, Markus Armbruster wrote:
If you're cc'ed, you added a section to docs/system/deprecated.rst that is old enough to permit removal. This is *not* a demand to remove, it's a polite request to consider whether the time for removal has come. Extra points for telling us in a reply. "We should remove, but I can't do it myself right now" is a valid answer. Let's review the file:
[adjusting cc for this response]
Eric Blake:
qemu-img amend to adjust backing file (since 5.1) '''''''''''''''''''''''''''''''''''''''''''''''''
The use of ``qemu-img amend`` to modify the name or format of a qcow2 backing image is deprecated; this functionality was never fully documented or tested, and interferes with other amend operations that need access to the original backing image (such as deciding whether a v3 zero cluster may be left unallocated when converting to a v2 image). Rather, any changes to the backing chain should be performed with ``qemu-img rebase -u`` either before or after the remaining changes being performed by amend, as appropriate.
qemu-img backing file without format (since 5.1) ''''''''''''''''''''''''''''''''''''''''''''''''
The use of ``qemu-img create``, ``qemu-img rebase``, or ``qemu-img convert`` to create or modify an image that depends on a backing file now recommends that an explicit backing format be provided. This is for safety: if QEMU probes a different format than what you thought, the data presented to the guest will be corrupt; similarly, presenting a raw image to a guest allows a potential security exploit if a future probe sees a non-raw image based on guest writes.
To avoid the warning message, or even future refusal to create an unsafe image, you must pass ``-o backing_fmt=`` (or the shorthand ``-F`` during create) to specify the intended backing format. You may use ``qemu-img rebase -u`` to retroactively add a backing format to an existing image. However, be aware that there are already potential security risks to blindly using ``qemu-img info`` to probe the format of an untrusted backing image, when deciding what format to add into an existing image.
I'm not sure how widely used these were, but I'm game for writing a patch to drop them. I'm fairly certain libvirt is not using them.
Kevin Wolf:
``nbd-server-add`` and ``nbd-server-remove`` (since 5.2) ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Use the more generic commands ``block-export-add`` and ``block-export-del`` instead. As part of this deprecation, where ``nbd-server-add`` used a single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
Peter, is libvirt good for this one to go? -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org