[libvirt] [RFC] Add flag for virsh undefine to remove/wipe the disk devices

[Osier Yang]

Hi, All

I'm thinking to introduce a new flag (something like --remove-disks,
--wipe-disks) for "virsh undefine", so that the user can choose
whether to remove/wipe the disk devices or not, have seen this
requirement in many places, @libvirt-users, public #virt, and also
we have a bug of this function. So, IMHO this is a reasonable
requirement, following is the rough thoughts:

1) General idea.
   As we don't have a API which can get all the disk devices of a
   domain, perhaps need to write functions to parse domain xml to
   extract the disks' path (this is annoyed, but seems don't other
   way), and then lookup them by storage volume API
   (virStorageVolLookupByPath), and then can remove or wipe
   the volume by (virStorageVolDelete/virStorageVolWipe).

   And for the disk path which doesn't belong to any storage pool,
   simply remove it by "unlink()"?

2) Which type of devices can not be removed/wiped.

   * Can't delete/wipe ISCSI/SCSI vol.
   * Vol doesn't exists (which will throw an warning when do
     virStorageVolLookupByPath).
   * Have no write permission on the parent directory of the
     disk path.
   * Can't delete/wipe the disk device which is passthrough'ed
     from host, (e.g. /dev/sr0 as a CDROM device for guest)
   * The storage pool which the disk device belongs to as a vol
     is marked as "share"
   * The storage pool which the disk device belongs as a vol is
     readonly
   * can't delete disk device of network type.
   * Any others?

   For these situations, we need to do checking and throw
   straightforward warnings to tell user why it can't be
   removed/wiped.

   Any idea is welcomed. Thanks.

   CC'ed Eric, as I saw you talked about this somewhere. (#virt?), :-)

Regards
Osier