Programming :: C- How To Skip Dirs That Are Mounted Twice

I need to list a directory recursively but I want to skip subdirs that were already mounted. There are 2 cases:

a) a filesystem was mounted twice, like in this example:

- "/dev/sda2" was mounted on "/mnt/mnt_point1"
- "/dev/sda2" was mounted on "/mnt/mnt_point2"

I want to list "/mnt" but descend only in "/mnt/mnt_point1"

b) part of the file hierarchy was remounted somewhere else, with "mount --bind":

- "mount --bind /home/user/tmp/test /home/user/tmp/mounted_test"

I want to list "/home/user/tmp" but descend only in "test" "statfs" and "statvfs" don't offer any information to discern if a dir was mounted twice. One solution would be to read "/etc/mtab" (as "find" command does it) and perform some checks, but I think that this is pretty expensive (one has to read /etc/mtab every time one encounters a dir; if this file is read only when program starts, a mount could occur in between reads, so that the program will be inaccurate). Another solution would be to filter kernel events (via libudev or Netlink) and do this reading of /etc/mtab only when a MOUNT event was issued.