Re: [Qemu-devel] [PATCH v2] Add support for fd: protocol

[Avi Kivity <avi@redhat.com>]

On 06/20/2011 04:50 PM, Anthony Liguori wrote:
> On 06/20/2011 08:40 AM, Avi Kivity wrote:
>> On 06/14/2011 04:31 PM, Corey Bryant wrote:
>>> - Starting Qemu with a backing file
>>>
>>
>> For this we could tell qemu that a file named "xyz" is available via fd
>> n, via an extension of the getfd command.
>>
>> For example
>>
>> (qemu) getfd path="/images/my-image.img"
>> (qemu) getfd path="/images/template.img"
>> (qemu) drive-add path="/images/my-image.img"
>>
>> The open() for my-image.img first looks up the name in the getfd
>> database, and finds it, so it returns the fd from there instead of
>> opening. It then opens the backing file ("template.img") and looks it up
>> again, and finds the second fd from the session.
>
> The way I've been thinking about this is:
>
>  -blockdev id=hd0-back,file=fd:4,format=raw \
>  -blockdev file=fd:3,format=qcow2,backing=hd0-back
>
> While your proposal is clever, it makes me a little nervous about 
> subtle security ramifications.

It would need careful explanation in the management tool author's guide, 
yes.

The main advantage is generality.  It doesn't assume that a file format 
has just one backing file, and doesn't require new syntax wherever a 
file is referred to indirectly.

-- 
error compiling committee.c: too many arguments to function