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'\" et
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.TH DIRFD "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.SH PROLOG
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This manual page is part of the POSIX Programmer's Manual.
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The Linux implementation of this interface may differ (consult
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the corresponding Linux manual page for details of Linux behavior),
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or the interface may not be implemented on Linux.
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.SH NAME
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dirfd
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\(em extract the file descriptor used by a DIR stream
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.SH SYNOPSIS
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.LP
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.nf
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#include <dirent.h>
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.P
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int dirfd(DIR *\fIdirp\fP);
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.fi
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.SH DESCRIPTION
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The
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\fIdirfd\fR()
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function shall return a file descriptor referring to the same directory
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as the
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.IR dirp
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argument. This file descriptor shall be closed by a call to
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\fIclosedir\fR().
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If any attempt is made to close the file descriptor, or to modify the
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state of the associated description, other than by means of
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\fIclosedir\fR(),
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\fIreaddir\fR(),
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\fIreaddir_r\fR(),
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\fIrewinddir\fR(),
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or
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\fIseekdir\fR(),
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the behavior is undefined.
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.SH "RETURN VALUE"
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Upon successful completion, the
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\fIdirfd\fR()
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function shall return an integer which contains a file descriptor for
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the stream pointed to by
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.IR dirp .
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Otherwise, it shall return \(mi1 and may set
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.IR errno
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to indicate the error.
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.SH ERRORS
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The
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\fIdirfd\fR()
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function may fail if:
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.TP
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.BR EINVAL
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The
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.IR dirp
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argument does not refer to a valid directory stream.
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.TP
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.BR ENOTSUP
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The implementation does not support the association of a file
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descriptor with a directory.
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.LP
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.IR "The following sections are informative."
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.SH EXAMPLES
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None.
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.SH "APPLICATION USAGE"
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The
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\fIdirfd\fR()
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function is intended to be a mechanism by which an application may
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obtain a file descriptor to use for the
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\fIfchdir\fR()
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function.
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.SH RATIONALE
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This interface was introduced because the Base Definitions volume of POSIX.1\(hy2008 does not make public
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the
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.BR DIR
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data structure. Applications tend to use the
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\fIfchdir\fR()
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function on the file descriptor returned by this interface, and this
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has proven useful for security reasons; in particular, it is a better
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technique than others where directory names might change.
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.P
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The description uses the term ``a file descriptor'' rather than ``the
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file descriptor''. The implication intended is that an implementation
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that does not use an
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.IR fd
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for
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\fIopendir\fR()
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could still
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\fIopen\fR()
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the directory to implement the
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\fIdirfd\fR()
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function. Such a descriptor must be closed later during a call to
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\fIclosedir\fR().
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.P
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An implementation that does not support file descriptors referring to
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directories may fail with
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.BR [ENOTSUP] .
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.P
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If it is necessary to allocate an
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.IR fd
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to be returned by
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\fIdirfd\fR(),
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it should be done at the time of a call to
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\fIopendir\fR().
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.SH "FUTURE DIRECTIONS"
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None.
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.SH "SEE ALSO"
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.IR "\fIclosedir\fR\^(\|)",
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.IR "\fIfchdir\fR\^(\|)",
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.IR "\fIfdopendir\fR\^(\|)",
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.IR "\fIfileno\fR\^(\|)",
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.IR "\fIopen\fR\^(\|)",
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.IR "\fIreaddir\fR\^(\|)"
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.P
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The Base Definitions volume of POSIX.1\(hy2008,
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.IR "\fB<dirent.h>\fP"
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 7, Copyright (C) 2013 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group.
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(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
|
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is the referee document. The original Standard can be obtained online at
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http://www.unix.org/online.html .
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Any typographical or formatting errors that appear
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in this page are most likely
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to have been introduced during the conversion of the source files to
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man page format. To report such errors, see
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https://www.kernel.org/doc/man-pages/reporting_bugs.html .
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