Re: [libvirt] [RFC] proposal for libiscsi storage pool
On Tue, Jun 05, 2018 at 09:37:06 +0200, Michal Privoznik wrote:
On 06/04/2018 05:54 PM, Clementine Hayat wrote:
> Hi everybody!
>
> I am starting this thread to discuss a new storage pool backend for
> iSCSI using libiSCSI.
Thanks a lot for working on this, I'm looking forward to switching to
the new pool.
> There already is an iSCSI backend, however, it uses iscsiadm
binary to
> execute the desired operation. The binary can be spawned multiple
> times during single execution of an API. This is suboptimal.
>
> Moreover the iscsi storage pool is mapped by the kernel into a block
> device in /dev/. Iscsiadm makes operations directly on that block
> device. Libiscsi on the other hand is sending the commands directly to
> a remote iscsi portal. According to that, to be able to use a storage
> pool using libiscsi we have to implement the storage pool backend
> entirely.
>
> What we would have:
>
> Pool XML using iscsiadm:
>
> <pool type="iscsi" mode="host">
This sounds reasonable. However, I think for backwards compatibility we
need to treat <pool type="iscsi"/> as mode="host". That is, if
we don't
parse any @mode, we must assume "host" and then we can format it into
the XML back.
On the other hand, we could perhaps just introduce a new pool type,
something like
<pool type='iscsi-direct'>...</pool>
which would match with VIR_STORAGE_POOL_ISCSI_DIRECT and avoid the black
magic of translating type="iscsi" to VIR_STORAGE_POOL_LIBISCSI or
VIR_STORAGE_POOL_ISCSI depending on the mode attribute. Not to mention
that old libvirt would just completely ignore the mode attribute, but it
would complain about unknown pool type.
Jirka