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- .TH DUP 3
- .SH NAME
- dup \- dups of open files
- .SH SYNOPSIS
- .nf
- .B bind #d /fd
- .B /fd/0
- .B /fd/0ctl
- .B /fd/1
- .B /fd/1ctl
- \&...
- .fi
- .SH DESCRIPTION
- The
- .I 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
- .I n
- corresponds to open file descriptor
- .I n
- in the current process.
- .PP
- An
- .IR open (2)
- of file
- .I n
- results in a file descriptor identical to
- what would be returned from a system call
- .IB dup ( n ,
- .BR -1) .
- Note that the result is no longer a file in the
- .I dup
- device.
- .PP
- The
- .I stat
- operation returns information about the device file, not the open file it points to.
- A stat of
- .BI #d/ n
- will contain
- .I 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.
- .PP
- A file of name
- .IB n ctl
- may be read to discover the properties of the associated file descriptor, in format identical to that of the
- .B fd
- file in
- .IR proc (3).
- .SH SEE ALSO
- .IR dup (2)
- .SH SOURCE
- .B /sys/src/9/port/devdup.c
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