Re: [Qemu-devel] format=raw,readonly errors

[Max Reitz <mreitz@redhat.com>]

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On 08.05.2017 18:33, Carl Karsten wrote:
> On Mon, May 8, 2017 at 11:29 AM, Eric Blake <eblake@redhat.com> wrote:
> 
>> On 05/08/2017 10:56 AM, Carl Karsten wrote:
>>
>>>>>>> juser@gator:~/temp$ qemu-system-x86_64 -m 256 -display curses
>> -drive
>>>>>>> file=disk.cow -drive file=boot.img
>>>>>>> WARNING: Image format was not specified for 'boot.img' and probing
>>>>>> guessed
>>>>>>> raw.
>>>>>>>          Automatically detecting the format is dangerous for raw
>>>> images,
>>>>>>> write operations on block 0 will be restricted.
>>>>>>>          Specify the 'raw' format explicitly to remove the
>>>> restrictions.
>>
>>>  "write operations on block 0 will be restricted."
>>>
>>> Is there a way to explicitly enable that?
>>
>> Yes. Pass format=raw at the right place (in other words, instead of
>> getting the 'raw' format driver by default, explicitly mentioning that
>> you KNOW you want the 'raw' format driver is enough to shut up the
>> warning).
>>
> 
> according to the warning: "Specify the 'raw' format explicitly to remove
> the restrictions."
> 
> I want the restriction.
> 
> format=raw, (write operations on block 0)=restricted

Well, the restriction won't prevent all writes to the first sector,
though; it will only prevent writes which would make the image look like
it was in some non-raw format. So this is probably not what you want anyway.

Unfortunately, I don't know any current way to "soft" write-protect an
image. It sounds like an interesting idea, though, and should be simple
enough to implement e.g. in the raw driver.

Max


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