DUP(3)                                                     DUP(3)

     NAME
          dup - dups of open files

     SYNOPSIS
          bind #d /fd

          /fd/0
          /fd/0ctl
          /fd/1
          /fd/1ctl
          ...

     DESCRIPTION
          The dup device serves a one-level directory containing files
          whose names are decimal numbers.  Each such file also has an
          associated control file.  A file of name n corresponds to
          open file descriptor n in the current process.

          An open(2) of file n results in a file descriptor identical
          to what would be returned from a system call dup(n, -1).
          Note that the result is no longer a file in the dup device.

          The stat operation returns information about the device
          file, not the open file it points to.  A stat of #d/n will
          contain n for the name, 0 for the length, and 0400, 0200, or
          0600 for the mode, depending on whether the dup target is
          open for reading, writing, or both.

          A file of name nctl may be read to discover the properties
          of the associated file descriptor, in format identical to
          that of the fd file in proc(3).

     SEE ALSO
          dup(2)

     SOURCE
          /sys/src/9/port/devdup.c

     Page 1                       Plan 9            (printed 12/22/24)