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Re: [Qemu-devel] [BUG] Regression: readonly raw images no longer work

From: Naphtali Sprei
Subject: Re: [Qemu-devel] [BUG] Regression: readonly raw images no longer work
Date: Mon, 22 Feb 2010 16:39:33 +0200
User-agent: Thunderbird (X11/20090817)

Stefan Weil wrote:
> This command used to work, but fails now:
> $ i386-softmmu/qemu -snapshot /dev/sda
> qemu: could not open disk image /dev/sda: Permission denied
> $ ls -l /dev/sda
> brw-rw-r-- 1 root disk 8, 0 13. Feb 08:55 /dev/sda
> The original file of a snapshot needs only read access,
> but QEMU tries read/write access and fails.
> Variants of above command using -hda or -drive
> also fail with the same error message.
> I did not test whether the regression affects other
> kinds of images, too. Maybe only raw images trigger
> no longer work.
> Regards
> Stefan Weil

Sorry for the late reply,
this is my fault. It will fail for any image format.

It's already fixed with commit 4dca4b639cb20fee38f6eec0a391aecc0ad8848d :
"block: more read-only changes, related to backing files"

Now, since the /dev/sda is the backing-file, it's opened as read-only, no 
permission problem.

Notice that if you try to commit your changes to the read-only disk (in monitor 
it will be silently ignored, no error or warning displayed.
Should I add a warning/error printing ? 


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