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Re: [Qemu-devel] [PATCH] Add tar container format
From: |
Christoph Hellwig |
Subject: |
Re: [Qemu-devel] [PATCH] Add tar container format |
Date: |
Sat, 15 Aug 2009 22:36:52 +0200 |
User-agent: |
Mutt/1.3.28i |
On Thu, Aug 13, 2009 at 06:13:27PM -0500, Anthony Liguori wrote:
> What's attractive about doing plugins for the block layer is that we
> have a relatively stable interface for block drivers. The current AIO
> ops should be good for a very long time so API churn shouldn't be a
> major issue. The code is all pretty well isolated today.
>
> As part of the longer term refactoring, I think it also makes sense to
> split the block layer into a library that can be consumed independent of
> QEMU. Obviously, folks want to make use of our block code who don't
> care at all about QEMU. A lot of people use qemu-img for vmdk
> manipulation, for instance. It also makes tools like qemu-iotest able
> to consume the block layer in a saner way.
>
> If others agree, I think we should start going down this road.
> block-tar/block-dictzip seem like obvious candidates for plugins.
Splitting drivers from the core is a total desaster, you'll end up with
the same crap as the X drivers vs core X server versioning mess. After
a long stabilization period we might be able to split the block layer
_including_ the drivers from qemu if we really want. Splitting the
drivers into tiny subpackages would be plain stupid.
As far as additional image formats are concerned I'm personally not a
fan at all of any of that image format crap we have right now. Anything
like qcow and friends or other formats that do complex metadata
manipulation in userspace is a really bad idea for data integrity.
Supporting simple containers with static metadata is absolutely fine,
even more so it it's read-only like the tar container here.
But one problem with tar is that there are many slightly or even totally
different tar formats and extensions around. It's not nessecarily a
format I would personally chose for a product. That's something the
SuSE stuio people should think about, but nothing that should prevent
us from including the format.