RS> Could you be more specific by the phrase of "block placement RS> decisions" what placement are you referring too? Sure. So, take a complex format like qcow for example. All of the data for the disk is in the file, but clearly not in linear order, right? Not only is it non-linear, but it's in some form that requires some understanding of a sophisticated set of metadata to linearize it. But, since the data is just jumbled up, we can use device-mapper to create a linear pseudo device that maps the linear blocks to their correct location in the qcow file. However, putting this logic in the kernel is mildly ugly, and gets extremely ugly when you talk about adding another format, such as vmdk, msvhd, etc. With dm-userspace and the help of my userspace application (cowd), you can mount these files as if they were normal disks in linux. So, by giving a userspace application real-time control over the mappings, we can push the complexity into userspace. There are a lot of other nifty things you can do from the comfort of userspace once you have this generic enabler in the kernel to act on your behalf. *Lots* :) -- Dan Smith IBM Linux Technology Center Open Hypervisor Team email: danms@xxxxxxxxxx
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