Re: [Qemu-devel] [PATCH 3/4] raw: Prohibit dangerous writes for probed images

[Eric Blake <eblake@redhat.com>]

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On 10/30/2014 06:26 AM, Kevin Wolf wrote:
> 
> The other differences of this patch to the old one are that it doesn't
> silently write something different than the guest requested by zeroing
> out some bytes (it fails the request instead) and that it doesn't
> maintain a list of signatures in the raw driver (it calls the usual
> probe function instead).
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block.c                   |  5 +++--

> +
> +        drv = bdrv_probe_all(buf, 512, NULL);
> +        if (drv != bs->drv) {
> +            ret = -EPERM;
> +            goto fail;
> +        }

So, what happens when this returns -EPERM?  If the guest is configured
to halt on write errors, does this halt the guest and send an event to
management?  How does it compare to the case of halting on ENOSPACE?  Is
this particular failure mode something that the host should be able to
easily distinguish from other failure modes?

But I definitely like that you only do this failure on probed images,
and that a user that requests an explicit raw format will never trip up.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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