Re: [Xen-devel] [PATCH RFC 0/4] tools: Upstream blktap "2.5" as an external repo

[Jon Ludlam <jonathan.ludlam@xxxxxxxxxx>]

On Thu, Mar 26, 2015 at 04:08:41PM +0000, George Dunlap wrote:
> On 03/26/2015 03:47 PM, Jon Ludlam wrote:
> > On Thu, Mar 26, 2015 at 12:46:06PM +0000, George Dunlap wrote:
> >> For some time, the blktap2 in-tree has bitrotted.  Many years ago the
> >> XenServer team at Citrix forked the code into a separate repository;
> >> several attempts have been made to upstream those changes back into
> >> Xen, to no avail.
> >>
> >> The blktap code at the moment is the only source of performant vhd
> >> format integration.  It's additionally in use by projects like the
> >> COLO project.
> >>
> >> This patch series removes the in-tree blktap2 code and treats the
> >> XenServer blktap tree as an upstream.  I've gotten agreement from the
> >> XenServer team to act as an upstream -- to accept patches fixing bugs,
> >> to help track down errors, and to attempt to help fix build breakages
> >> introduced by development.
> >>
> >> At the moment we're using the "blktap2" branch of XenServer's
> >> blktap.git.  (This has been sometimes known as "blktap 2.5".)  This
> >> branch is maintianed in order to provide a buildroot for OpenStack,
> >> and has also been used by the CentOS xen packages for several years
> >> now.
> > 
> > It's probably worth mentioning again that there is a kernel patch
> > required. Some years ago I did some work to make the patch into a dkms
> > module, but since then the patch and the kernel have moved on and I
> > couldn't quite make it work any more; I'm afraid my kernel knowledge
> > is a bit lacking.
> > 
> > The current patches used in XenServer are on github here:
> > https://github.com/xenserver/linux-3.x.pg/tree/master/master
> > 
> > and the old dkms code is here:
> > https://github.com/xapi-project/blktap-dkms
> > 
> > In case anyone is interested...!
> 
> Another thing I'd like to explore (since this took all of about an
> afternoon to get working) is what it would take to switch to using
> blktap3 instead.  As I understand from my conversations with the
> XenServer team, they use a kernel module in XenServer when mounting an
> image in dom0 for scalability reasons; but there's no reason XenProject
> need to do the same thing.
> 
> I'd probably need some guidance from the XenServer team about an
> appropriate way to start that. :-)
>

Good question. The right people to speak to are probably Germano and/or
Felipe (cc'd)

Jon


>  -George

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