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

Kevin Wolf wrote:
> So what I'm saying is that while I'm not opposed to a rewrite in
> principle, the rewrite needs to be a complete drop-in replacement to
> avoid this third copy of the code. Ideally the rewrite would be
> completely integrated into qemu, but at least not having a third copy
> and making things even worse is a must, IMHO.

Oh, btw:  qemu itself will get a xen block backend implementation soon

Patch queue against qemu svn (upstream) are here:

Patch queue for the qemu-xen git tree are here:

The patch adding the block backend is this one:

You might also look at this one (common xenbus state machine, ...):

Merging those patch sets into both qemu trees will start when Ian
Jackson (qemu-xen maintainer) is back.

Note that a special kernel driver for blktap isn't needed at all.  You
can simply use the generic grant table and event channel device drivers.
   Which is exactly what the qemu backend implementation does.  IMHO the
blktap kernel driver is there only for historical reasons (it predates
gntdev) and it should go away long-term.

The qemu block layer has some problems performance-wise, so I can see
your reasons to not use qemu.  And the qemu backend will most likely not
(yet) match blktap performance-wise.  Nevertheless I think time is
better spent fixing these problems in upstream qemu instead of forking
off the qemu block layer code for the tapdisk daemon.


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