DragonFly On-Line Manual Pages  FDESC(5)
DragonFly File Formats Manual                FDESC(5)   fdesc --
file-descriptor file system   fdesc /dev fdesc rw 0 0   The
file-descriptor file system, or fdesc, provides access to the
per- process file descriptor namespace in the global filesystem
namespace. The conventional mount point is /dev and the
filesystem should be union mounted in order to augment, rather
than replace, the existing entries in /dev. The contents of the
mount point are fd, stderr, stdin, stdout and tty. fd is a
directory whose contents appear as a list of numbered files
which correspond to the open files of the process reading the
directory. The files /dev/fd/0 through /dev/fd/# refer to file
descriptors which can be accessed through the file system. If
the file descriptor is open and the mode the file is being
opened with is a subset of the mode of the exist- ing
descriptor, the call: fd = open("/dev/fd/0", mode); and the
call: fd = fcntl(0, F_DUPFD, 0); are equivalent. The files
/dev/stdin, /dev/