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

On Wed, Jan 27, 2016 at 02:25:51PM -0600, 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. 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 believe what Jim is saying that there needs to be some parsing in libxl
so that it can pass the right information to QEMU. But that is an assumption
and it may be that we do not need it as you suggest?

> -- 
> Doug Goldstein

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