minix/lib/nbsd_libc/sys/dup.2
Gianluca Guida b6cbf7203b Import unmodified NetBSD libc in trunk
This patch imports the unmodified current version of NetBSD libc.
The NetBSD includes are in /nbsd_include, while the libc code itself is 
split between lib/nbsd_libc and common/lib/libc.
2011-02-14 19:36:03 +00:00

138 lines
3.7 KiB
Groff

.\" $NetBSD: dup.2,v 1.21 2009/01/11 02:46:30 christos Exp $
.\"
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.\" @(#)dup.2 8.1 (Berkeley) 6/4/93
.\"
.Dd December 2, 2008
.Dt DUP 2
.Os
.Sh NAME
.Nm dup ,
.Nm dup2
.Nd duplicate an existing file descriptor
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn dup "int oldd"
.Ft int
.Fn dup2 "int oldd" "int newd"
.Sh DESCRIPTION
.Fn dup
duplicates an existing object descriptor and returns its value to
the calling process
.Fa ( newd
=
.Fn dup oldd ) .
The argument
.Fa oldd
is a small non-negative integer index in
the per-process descriptor table.
The value must be less than the size of the table, which is returned by
.Xr getdtablesize 3 .
The new descriptor returned by the call
is the lowest numbered descriptor currently not in use by the process.
.Pp
The object referenced by the descriptor does not distinguish
between
.Fa oldd
and
.Fa newd
in any way.
Thus if
.Fa newd
and
.Fa oldd
are duplicate references to an open
file,
.Xr read 2 ,
.Xr write 2
and
.Xr lseek 2
calls all move a single pointer into the file,
and append mode, non-blocking I/O and asynchronous I/O options
are shared between the references.
If a separate pointer into the file is desired, a different
object reference to the file must be obtained by issuing an
additional
.Xr open 2
call.
The close-on-exec flag on the new file descriptor is unset.
.Pp
In
.Fn dup2 ,
the value of the new descriptor
.Fa newd
is specified.
If this descriptor is already
in use, the descriptor is first deallocated as if a
.Xr close 2
call had been done first.
If
.Fa newd
and
.Fa oldd
are the same, the call has no effect.
.Sh RETURN VALUES
The value \-1 is returned if an error occurs in either call.
The external variable
.Va errno
indicates the cause of the error.
.Sh ERRORS
.Fn dup
and
.Fn dup2
fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa oldd
is not a valid active descriptor
or
.Fa newd
is not in the range of valid file descriptors.
.It Bq Er EMFILE
Too many descriptors are active.
.El
.Sh SEE ALSO
.Xr accept 2 ,
.Xr close 2 ,
.Xr fcntl 2 ,
.Xr open 2 ,
.Xr pipe 2 ,
.Xr socket 2 ,
.Xr socketpair 2 ,
.Xr getdtablesize 3
.Sh STANDARDS
The
.Fn dup
and
.Fn dup2
functions conform to
.St -p1003.1-90 .