Re: [Xen-devel] [4 Patches] New blktap implementation, 2nd try

[Dutch Meyer <dmeyer@xxxxxxxxx>]

> Why would you want to keep the old version around if the new one is so
> much better?
We're very open to removing the old version, but there is a backwards 
compatability concern.  See below.
> Now this is a huge patch, nearly impossible to review. At a first glance
> I noticed that it shares large parts with the old implementation. So
> while I believe you that the first patch is only moving things around, I
> really can't tell what this patch is actually doing.
I think relative to the changes, there isn't that much that is shared with 
the old implementation.  Taking a diff against the two directories will 
show that the core of blktap has been redone, much of it from scratch. 
That's why we did it this way.
You can diff versus the two blktap directories to see this.  If you still 
think this would be very helpful, I can provide this diff.  The drivers 
are, at their core, unchanged so perhaps separate patches would make sense 
in that case.
> I didn't really look into the patch but merely scrolled through it and
> looked at the diffstat, so maybe I'm wrong, but it seems to lack
> implementations for tap:qcow2, tap:vmdk and tap:ioemu. Why that?
You're right about that - we decided to post this without qcow2, but can 
port that one as well.  VMDK is slow, it's written to be purely 
synchronous, and we don't think anyone actually uses it.
ioemu is a different matter - This is a very difficult piece of code to 
work with, because large portions of blktap have been replicated to make 
it work.  On top of that, the wire protocol changed to support this. 
Porting this driver would be quite difficult.  This ioemu code is the 
primary reason we provided backwards compatability with what is now 
"blktap_old".

I really appreciate the conversation here, and look forward to keeping it 
going, but i may be away from email for the weekend, so please excuse any 
slowness in my reply.
--Dutch

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