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Date: Mon, 01 Feb 2010 09:46:00 +0100
From: Kevin Wolf <kwolf@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH] block: Enable fall-back to read-only for
	backing file
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To: Naphtali Sprei <nsprei@redhat.com>
Cc: qemu-devel@nongnu.org, Sheng Yang <sheng@linux.intel.com>

Am 31.01.2010 17:49, schrieb Naphtali Sprei:
> There's a problem when trying to use an image file based on a read-only image file.
> Before this patch, qemu fails to open the base image and stop.
> With this patch, qemu tries to open the backing file with same permissions as the "top" file,
> but if it fails, qemu tries to open it with read-only permissions. If succeeded it goes on.
> 
> This fall-back works both for an image file based on a read-only file
> and also for a read-only file opened with the snapshot attribute/mode (where the real file is the backing file
> for the snapshot file).
> 
> Is it better to always open the backing file with read-only mode ? this will be more consistent/predictable ?

I would love to open them read-only unconditionally, but we can't. It
would break the commit monitor command. I think the read-only fallback
is appropriate for backing files.

Kevin