Re: [Xen-devel] [PATCH 8/8] raisin: RFC Add blktap2 as an external tree

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 21 Apr 2015, George Dunlap wrote:
> On 04/21/2015 10:25 AM, Ian Campbell wrote:
> > On Mon, 2015-04-20 at 18:05 +0100, Stefano Stabellini wrote:
> >>>> I think we need to disable the build on architectures other than x86,
> >>>> see grub for example
> > 
> > Eventually we might want to build our own grub on ARM in order to pick
> > up Fu Wei's multiboot for arm64 patches, until they enter distros?
> > 
> > Or maybe Raisin on UEFI should be calling efibootmgr to register Xen
> > directly with the BIOS, and creating a xen.cfg in /boot, i.e. the way it
> > currently works even on x86.
> > 
> >>> Do we?  There's no reason a blktap2 kernel module couldn't be built on
> >>> ARM, is there?
> >>
> >> Maybe not, but I am pretty sure that it doesn't work at the moment. I
> >> don't think that the userspace stuff even compiles on ARM.
> >> Eventually we might have blktap on ARM, but I don't want to enable
> >> stuff in Raisin that we know it does not work.
> > 
> > Especially if it is already to a greater or lesser extent deprecated (in
> > favour of eventual blktap3) even on x86.
> 
> So from my discussions w/ the XenServer guys, it seems that:
> 
> 1. The "master" branch of the blktap.git repo contains support for
> *both* blktap3 and blktap2.5 (with a kernel module)
> 
> 2. XenServer uses blktap3 for guest access, but still use the blktap2.5
> w/ kernel module for dom0 access to guest disks, to avoid the
> possibility of hitting a scalability limit due to grant references.
> 
> So from raisin's perspective, the only difference between blktap2.5 and
> blktap3 is using the "master" branch rather than the "blktap2" branch of
> the repo.

That is not entirely true: compiling and installing a kernel module is
quite different from userspace stuff, at least in terms of dependencies
and installation paths.


> Whether we maintain support for blktap2.5 in libxl is a matter for the
> Xen maintainers; but if xapi is ever going to start using libxl, it will
> certainly need to be able to do so.
> 
> (Dave / David, please correct me if I'm wrong.)
> 
> That said, there's no harm in disabling it on ARM to begin with, and
> enabling it once blktap3 works.

Yes, I would the code in Raisin to actually work :-)

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