Re: The future of blktap in Xen4CentOS

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Hello,

On Wed, May 06, 2015 at 03:27:54PM +0100, George Dunlap wrote:
> On Tue, May 5, 2015 at 2:07 PM, Johnny Hughes <johnny@xxxxxxxxxx> wrote:
> > WRT a new kernel .. the 3.18.x kernel has been selected to be maintained
> > as an LTS until Jan 2017.  I think we should start work on rebuilding
> > this kernel and using it in the x4c projects.
> >
> > https://lwn.net/Articles/636289/
> >
> > Thoughts?
> >
> > I will grab this kernel and try to roll in all the patches, etc. and see
> > if I can make it work.
> 
> I did a little bit of work on building the 3.18 kernel a couple of
> weeks ago, but it looks like the blktap2.5 kernel code we were using
> before has totally bitrotted.
> 
> I see three ways forward:
> 
> 1. Try to do a "deep port" of the functionality, continuing to
> maintain it going forward.
>

How badly has the blktap 2.5 kernel code bitrotted? What areas are the most problematic?
Any idea how much work would it be to get it working with 3.18 LTS ? 

 
> 2. Start using the blktap3 code, which requires no kernel driver.
> 
> 3. Drop blktap support, and ask people to use qdisk for vhd.
> 
> Re #1, I'm not really excited about the idea of trying to keep porting
> those patches forward (and finding and fixing bugs in the forward-port
> each time).
> 
> Re #2, this would require getting the blktap3 stuff working upstream
> and then backporting it.
> 

Yeah.. likely more work than the "deep port" of blktap 2.5 kernel code..

> #3 would be by far the easiest.
>

But not very nice.. 
 
> In parallel to the Xen for C7 work I've been doing, I've been working
> on getting upstream Xen to build against XenServer's blktap code, with
> then aim of moving to blktap3.  If we want to go with #2, then a major
> kernel update will have to wait until that work is done.
>
>  -George


Thanks,

-- Pasi

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