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Date: Wed, 07 Apr 2010 14:32:34 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] block: reject O_RDWR open for read-only
	images
References: <20100407115753.GB12452@lst.de>
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To: Christoph Hellwig <hch@lst.de>
Cc: qemu-devel@nongnu.org

Am 07.04.2010 13:57, schrieb Christoph Hellwig:
> Various obscure image format drivers do not allow write access.
> Instead of silently falling back to read-only access reject attempts
> to open these images for write access.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

I'm not sure about this patch. I don't have any such images around, so I
can't test it easily, but it looks to me as if you'd need to explicitly
specify readonly=on if you want to use such formats. This in turn means
that old style shortcuts like -hda don't work any more. Is it that
important to avoid implicit fallbacks for obscure formats that we're
willing to sacrifice compatibility?

That said, personally I don't care about those format all that much
anyway and the change would make things more consistent. If people
consider it okay to break compatibility in this way, I won't stand in
your way.

But if we wanted to implement this, have you thought about doing it in
one place in block.c? You could check if a driver supports bdrv_write or
bdrv_aio_write, and if it doesn't support either I think you can assume
it's read-only.

Kevin