This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


[Xen-devel] Re: [5 Patches] Synchronize blktap with citrix blktap2.

To: Ben Guthro <ben.guthro@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [5 Patches] Synchronize blktap with citrix blktap2.
From: Dutch Meyer <dmeyer@xxxxxxxxx>
Date: Fri, 3 Apr 2009 08:28:15 -0700 (PDT)
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date: Fri, 03 Apr 2009 08:28:39 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <1238770391.6535.52.camel@bguthro-desktop>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <1238770391.6535.52.camel@bguthro-desktop>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
You've got the right idea, but it's no problem. If you're using blktap2 (eg tap:tapdisk:aio:...) the usermode scripts will create a new udev device for the guest to mount. This is entirely orthogonal to qemu, so there's no problem.

If the qemu folks wanted to use blktap2 they could have the guest mount a blktap2 disk like it was any other raw device. However, they've decided to instead replicate the original blktap functionality in their own code base. So if you're using qemu's blktap you're not using blktap2. Again, not a problem.


On Fri, 3 Apr 2009, Ben Guthro wrote:

I started to look into these patches, to try to evaluate how much
performance improvement this re-write gives, but have a problem with the
way this works.

As I understand the patch set in userspace you:
1. move the old blktap dir to blktap_old
2. introduce the new blktap2 code in blktap

However, these changes that you are making to qemu merely link against
the old libraries, rather than adjusting the include paths to include
the new headers, and compile/link against the new blktap2?

Won't this cause problems when you actually go to use tapdisk?

Am I missing something here?


       I've been reminded that the ioemu patch to update the blktap 
dependencies in that repo is still necessary. It is available here:


Xen-devel mailing list