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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

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. :-)

 -George

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