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Date: Mon, 15 Mar 2010 11:23:38 +0100
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] -fda fat:dir -snapshot
References: <4B9BE4F1.6030202@msgid.tls.msk.ru>
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To: Michael Tokarev <mjt@tls.msk.ru>
Cc: qemu-devel <qemu-devel@nongnu.org>

Am 13.03.2010 20:18, schrieb Michael Tokarev:
> Apparently this does not work, and for a loooong time:
> 
>  $ kvm -fda fat:dir
>  [ it opens the sdl window ]
>  $ kvm -fda fat:dir -snapshot
>  qemu: could not open disk image fat:dir: No such file or directory
> 
> Is it supposed to work?

Wow, that's a crazy case. I guess nobody has ever tested this, and
indeed it looks like it never has worked. As you might know, -snapshot
internally creates a temporary qcow2 image which takes the image you
originally asked for as a backing file.

So we have a qcow2 file with a backing file tmp:dir. Now, backing file
paths are always resolved relative to the COW file, so we get
/tmp/fat:dir. Oops.

We could just disable this for protocols as a quick fix, but I think in
fact you do want to have this behaviour when using protocols as a
backing file for a persistent COW image. I guess this needs some more
thought, especially in respect to the discussions of making
file/host_device/... protocols.

If you really have a use case for this, you can use an absolute path
after fat: as a workaround, it won't touch the path then.

Kevin