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

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.