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

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.

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