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

[Dutch Meyer <dmeyer@xxxxxxxxx>]

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.
--Dutch

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?
>
> Ben
>
>
>        I've been reminded that the ioemu patch to update the blktap 
> dependencies in that repo is still necessary. It is available here:
>        http://www.cs.ubc.ca/~dmeyer/blktap2/tools_ioemu_dir_use_blktap_old.patch
>
>        --Dutch
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