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Date: Mon, 6 Jul 2009 12:20:24 +0200
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] [PATCH] qemu-io: add flag to mark files growable
Message-ID: <20090706102023.GA7835@lst.de>
References: <20090704155330.GA4825@lst.de> <4A51BBA1.4090307@redhat.com>
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To: Kevin Wolf <kwolf@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, qemu-devel@nongnu.org

On Mon, Jul 06, 2009 at 10:53:53AM +0200, Kevin Wolf wrote:
> Christoph Hellwig schrieb:
> > Add a -g flag to the open command and the main qemu-io command line to
> > allow opening a file growable.  This is only allowed for protocols,
> > mirroring the limitation exposed through bdrv_file_open.
> 
> This limitation doesn't look quite right. I'm not sure if growable
> images are used anywhere else, too, but their main usage is for the
> image file access in formats like qcow - that is, growable images are
> usually raw. And raw didn't have a protocol name until recently.

It does have a protocol now, and the way current qemu is implemented
growable is only set from bdrv_file_open, which implies the BDRV_O_FILE
argument to bdrv_open2, which means we use find_protocol to find the
BlockDriver and find_protocol needs protocol_name set.

If you want to backport this patch to a qemu version that doesn't
have a protocol_name for raw you'll have to adjust it to whatever check
is correct in that version.