[libvirt] [PATCH 2/2] storage: Forbid wiping formatted volume types that are not supported

[Ján Tomko]

On Thu, Jul 14, 2016 at 02:27:41PM +0200, Martin Kletzander wrote:
>Until now we allowed that to happen, however the only thing we supported
>was either rewiting the file or truncating it.  That however doesn't
>keep the format of that file, so QCOWs, VDIs and all others just became
>RAW with arbitrary size. 

Yes, wiping wipes the format as well. Nothing wrong with that.

> Not to mention any domain using such volume
>could not start anymore.  Instead of dealing with the recreation of
>every single possible file that we have (and possibly failing due to
>create_tool capabilities) just forbid it for now.

> We even state in our
>documentation that it has no value for file-backed volumes.
>

Where?

  Also note, that depending on the actual volume representation, this call
  may not really overwrite the physical location of the volume. For
  instance, files stored journaled, log structured, copy-on-write,
  versioned, and network file systems are known to be problematic.

http://libvirt.org/html/libvirt-libvirt-storage.html#virStorageVolWipe

This only says that it might not work, not that it's completely useless.

I think we have a precedent for supporting marginally useful features by
still supporting qcow encryption.

>Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=868771
>

NACK to breaking functionality in order to resolve a 4-year-old
synthetic QE-filed bug.

I suggest WONTFIX or NOTABUG.

Jan