Re: [Xen-devel] [RFC] support more qdisk types

[Doug Goldstein <cardoe@xxxxxxxxxx>]

On 1/27/16 8:37 PM, Jim Fehlig wrote:
> On 01/27/2016 01:25 PM, Doug Goldstein wrote:
>> On 1/27/16 12:32 PM, Konrad Rzeszutek Wilk wrote:
>>> On Mon, Jan 25, 2016 at 05:25:02PM -0700, Jim Fehlig wrote:
>>>> I would like to hear the community's opinion on supporting more qdisk 
>>>> types in
>>>> xl/libxl, e.g. nbd, rbd, iSCSI, etc. I prefer supporting additional qdisk 
>>>> types
>>>> in libxl over apps like xl or libvirt doing all the setup, producing a 
>>>> block
>>>> device, and then passing that to libxl. Each libxl app would have to
>>>> re-implement functionality already provided by qdisk. libxl already 
>>>> supports
>>>> IDE, AHCI, SCSI, and Xen PV qdisks. My suggestion is to extend that to 
>>>> initially
>>>> include nbd, rbd, and iSCSI. Sheepdog, ssh, etc. could be added in the 
>>>> future.
>>> ssh?
>>>> I considered several approaches to supporting additional qdisk types, based
>>>> primarily on changes to the disk cfg and interface. At one extreme is to 
>>>> change
>>>> nothing and use the existing 'target=' to encode all required config for 
>>>> the
>>>> additional qdisk types. libxl would need to be taught how to turn the blob 
>>>> into
>>>> an appropriate qdisk. At the other extreme is extending 
>>>> xl-disk-configuration
>>> Either way - new backends would require changes in both libxl and libvirt 
>>> right?
>>> The libxl would need to understand the new 'target=' blob to parse it out?
>>>
>> libvirt would probably just do what its doing now. Since it can setup
>> the connection and pass the file descriptor into libxl.
> 
> Hmm, I'm not sure I understand. AFAIK, there is no way to pass libxl a file
> descriptor opened from an image file or block device.
> 
>>  Honestly I don't
>> see the advantage here because libvirt does a better job from a security
>> standpoint and unless the goal is to have everything and the kitchen
>> sink in libxl/xl. There's already a number of ways to skin the cat (xl,
>> libvirt, xapi, openstack), why another one?
> 
> I'm simply proposing to extend the types of devices supported by and already
> supported backend - qdisk. libxl configures qdisk based on the contents of the
> libxl_device_disk struct. This proposal extends the struct with info necessary
> to support the additional qdisk types.
> 
> Regards,
> Jim
> 

Well I apologize for my comments because I clearly didn't understand
what you were proposing. Sounds good.

-- 
Doug Goldstein

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