On Fri, Apr 01, 2011 at 12:51:41PM +0100, Jean-Yves Migeon wrote:>I'm not sure this is the right way to do it; performance-wise. It's the only one reasonable for now, as they can be handled directly within a process. Otherwise, we have to make somekind of "vnd(4)" plugin, and implement sparse support (which is not as easy as it seems).I'm probably missing something here. Why do we need one process (qemu-dm)talking to another process to do I/O
The purpose is rather to support file formats that can offer block device functionality, without having to (re)write their support directly in kernel. AFAICT, vnd(4) does not support sparse files, and qcow/raw formats are sparse. The quickest way to expose those through a vnd(4) like interface is probably qemu-dm + pud(4).
Same goes for other kind of fs too, like vmdk, compressed images, etc. -- Jean-Yves Migeon jeanyves.migeon%free.fr@localhost