Re: [Qemu-devel] qemu-img convert with block driver without .bdrv_create (like iscsi)

[ronnie sahlberg]

On Thu, Oct 25, 2012 at 6:58 AM, Paolo Bonzini <address@hidden> wrote:
> Il 25/10/2012 15:41, ronnie sahlberg ha scritto:
>> On Thu, Oct 25, 2012 at 1:02 AM, Kevin Wolf <address@hidden> wrote:
>>> Am 25.10.2012 09:52, schrieb Paolo Bonzini:
>>>> Il 25/10/2012 09:46, Kevin Wolf ha scritto:
>>>>>>> 1)add a .bdrv_create in block/iscsi.c ?
>>>>>>>
>>>>>>> (like host_device block driver, only open/close the device and check if 
>>>>>>> size if big enough)
>>>>> Yes, this is the right way.
>>>>
>>>> Could it be a default implementation of .bdrv_create (i.e. something
>>>> you'd do in bdrv_create if the protocol doesn't have it)?
>>>
>>> No, there are block drivers that really can't create images. They should
>>> keep failing.
>>
>> Technically, you can not create new LUNs via the iscsi protocol
>> itself, you can only access pre-existing luns
>> that have been created by some out-of-band method.
>>
>> So basically, with iscsi you can only ever access already preexisting luns.
>>
>> In that case I think requiring a .bdrv_create feels wrong. We are not
>> creating a new LUN here but just opening an already existing LUN.
>
> The problem is that bdrv_create is overloaded to mean both "create the
> backing storage" and "format the image".  Only the latter applies to
> iSCSI and, in general, as far as protocols are concerned bdrv_create is
> usually a no-op.
>
> However, Kevin said he prefers to have an explicit override of
> bdrv_create for iSCSI.  Can you implement that?  (I'll then do the same
> for NBD).
>

Yepp. Since there is consensus.
We can do a .bdrv_create for iscsi.c

regards
ronnie sahlberg