On 24 Mar 2016, at 09:33, Wouter Verhelst wrote: > Now I'm not saying we > need to fully define what it means for a part of the backend to be > "dirty" or not. It's okay to leave part of the meaning in the dark, > leaving that implementation-defined. Well, the 3 possible states are: * unallocated * zero * non-zero So the possible replies are a bitfield of those, with a '1' if it 'might' be in that state, i.e. 111 = no idea 110 = might be zero or unallocated, but isn't zero 011 = I know it's allocated, but I don't know whether it is zero or not And '000' is not permitted! etc. -- Alex Bligh