[libvirt] [PATCH] storage: Document wiping formatted volume types

[Martin Kletzander]

When wiping a volume we just rewrite all the data of the volume, not
only the content.  Since format gets overriden, we need to recreate the
volume.  However we can't do that for every possible format there.  And
since it was only coded for the ploop volume type, let's document what
might be the consequences instead of forbidding it for every other
format out there.

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

Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
---
 src/libvirt-storage.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/libvirt-storage.c b/src/libvirt-storage.c
index cebe02fdda66..2be95a5adcaf 100644
--- a/src/libvirt-storage.c
+++ b/src/libvirt-storage.c
@@ -1732,6 +1732,12 @@ virStorageVolDelete(virStorageVolPtr vol,
  * journaled, log structured, copy-on-write, versioned, and
  * network file systems are known to be problematic.
  *
+ * NB the data includes the format (and possibly size information), so
+ * non-raw images might become raw with different size from libvirt's
+ * POV.  Due to the fact that not all information for re-creating the
+ * volume can be kept for every volume type, the volume might be kept
+ * in that state and not re-created.
+ *
  * Returns 0 on success, or -1 on error
  */
 int
-- 
2.9.2