Ludo', On 18/07/17 13:49, Ludovic Courtès wrote: > What about generating a UUID in a deterministic yet somewhat unique > fashion along these lines (untested):
Not great, but I can't think of a better way. :-) > + (define root-uuid > + ;; UUID of the root file system, computed in a deterministic fashion. > + (if (string=? "iso9660" file-system-type) > + (let ((pad (compose (cut string-pad <> 2 #\0) > + number->string))) > + (string->iso9660-uuid > + (string-append "1970-01-01-" > + (pad (hash name 24)) > + (pad (hash file-system-type 60)) > + (pad (hash (operating-system-host-name os) 60))))) > + (uint-list->bytevector > + (list (hash (string-append file-system-type name) > + (expt 2 64)) > + (hash (operating-system-host-name os) > + (expt 2 64))) > + (endianness little) > + 8))) > + Why not throw SIZE into this mix as well? When building without ‘--image-size’ (the default nowadays), it's a function of the exact size of the entire graph and reasonably sensitive to most kinds of input changes. > We cannot use the store file name’s hash, unfortunately, because the > UUID has to be given on the “host side.” That is unfortunate, but a best-effort heuristic will do. Kind regards, T G-R
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