[This interface is based on what is described in version 3 of a patchset for close_range() to lkml -- I would wait for it to be accepted and merged before committing...]
close_range(min, max, flags) allows for a range of descriptors to be closed. The Python folk have indicated that they would much prefer this interface to closefrom(2), as the case may be that they/someone have special fds dup'd to higher in the range and they can't necessarily closefrom(min) because they don't want to hit the upper range, but relocating them to lower isn't necessarily feasible.
sys_closefrom has been rewritten to use kern_close_range() using ~0U to indicate closing to the end of the range. This was chosen rather than requiring callers of kern_close_range() to hold FILEDESC_SLOCK across the call to kern_close_range for simplicity.
The flags argument of close_range(2) is currently unused, so any flags set is currently EINVAL. It was added to the interface in Linux so that future flags could be added for, e.g., "halt on first error" and things of this nature.
 I'm not averse to changing it at all...