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.

          A sys-open(2) of file n results in a file descriptor identi-
          cal to what would be returned from a system call sys->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 400, 200, or
          600 (octal) for the mode, depending on whether the dup tar-
          get 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 prog(3).

     SEE ALSO
          sys-dup(2)

     SOURCE
          /usr/inferno/emu/port/devdup.c
          /usr/inferno/os/port/devdup.c

     Page 1                       Plan 9             (printed 2/16/26)