Re: [PATCH v2] kvm tool: add QCOW verions 1 read/write support

[Anthony Liguori <anthony@codemonkey.ws>]

On 04/14/2011 03:52 AM, Kevin Wolf wrote:
>
> Well, copying in itself is not a big problem as long as the copies are
> kept in sync. It's a bit painful, but manageable. Implementing every
> image format twice (and implementing image formats in a reliable and
> performing way isn't trivial) is much more painful.
>
> If you take the approach of "getting inspired" by qemu and then writing
> your own code, the code will read pretty much the same, but be different
> enough that a diff between both trees is useless and a patch against one
> tree is meaningless for the other one.
>
> The block drivers are relatively isolated in qemu, so I think they
> wouldn't pull in too many dependencies.

The block layer has some interesting bits though that I can understand 
wanting to avoid (like aio emulation).

In the very least, we've learned the hard way that getting an image 
format right is very hard.  A good test suite is worth it's weight in 
gold for something like this.   When taking the approach of starting 
fresh, doing test driven development is definitely worth considering.

Regards,

Anthony Liguori

> Kevin
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