Hi, So yesterday I implemented the fallocate(FALLOC_FL_PUNCH_HOLE) stuff for NBD_CMD_TRIM. It's compile-tested, but not yet functionally tested. To be honest, I'm not entirely sure how to test whether a file is sparse in a particular region; anyone? Anyway, reviews on that short piece of code are obviously welcome. -- The volume of a pizza of thickness a and radius z can be described by the following formula: pi zz a