Will Thompson authored
The previously implementation considered a file to be a mountpoint if its parent is on a different device. / is its own parent, so by this definition it is not a mountpoint. But / is (generally) listed in fstab, and fstab(5) defines the directories it contains to be mountpoints. This attribute should follow that definition (and reasonable expectation): the root directory is a mountpoint. So, add a special-case for the case where the file's parent has the same st_dev and st_ino as the file, which is true only at the root. Test this attribute at / (only on POSIX), /proc (but only on Linux), and at many files and directories created by the test suite (which cannot be mountpoints).