fallocate(..., FALLOC_FL_COLLAPSE_RANGE) will do that but it comes with limitations such as alignment requirements and limited filesystem support. You could al

fallocate(..., FALLOC_FL_COLLAPSE_RANGE) will do that but it comes with limitations such as alignment requirements and limited filesystem support. You could also try creating a new file and use copy_file_range to copy the tail of the file to the new one, then move it over the old one. That might reuse a good chunk of the storage on a CoW filesystem.