This may sound like a silly question but up until recently if you tried to unmount a volume that was in use the Finder reported that it was in use, but not by whom. This is simple Unix functionality, if a file is open on a mount point, do not allow it to eject. But now they seem to have added functionality that lets the user know what programs are currently using a mounted system, and I have been looking through man pages of fopen,stat, etc. for Unix like operating systems(distros of linux) and I can't seem to find similar functionality.
Is this functionality specialized, or am I just looking in the wrong place?