.\" Copyright (C) 2003 John Levon <levon@movementarian.org>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" Modified 2004-06-17 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.TH lookup_dcookie 2 2024-05-02 "Linux man-pages 6.8"
.SH NAME
lookup_dcookie \- return a directory entry's path
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.BR "#include <sys/syscall.h>" "      /* Definition of " SYS_* " constants */"
.B #include <unistd.h>
.P
.BI "int syscall(SYS_lookup_dcookie, uint64_t " cookie ", char *" buffer ,
.BI "            size_t " len );
.fi
.P
.IR Note :
glibc provides no wrapper for
.BR lookup_dcookie (),
necessitating the use of
.BR syscall (2).
.SH DESCRIPTION
Look up the full path of the directory entry specified by the value
.IR cookie .
The cookie is an opaque identifier uniquely identifying a particular
directory entry.
The buffer given is filled in with the full path of the directory entry.
.P
For
.BR lookup_dcookie ()
to return successfully,
the kernel must still hold a cookie reference to the directory entry.
.SH RETURN VALUE
On success,
.BR lookup_dcookie ()
returns the length of the path string copied into the buffer.
On error, \-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EFAULT
The buffer was not valid.
.TP
.B EINVAL
The kernel has no registered cookie/directory entry mappings at the
time of lookup, or the cookie does not refer to a valid directory entry.
.TP
.B ENAMETOOLONG
The name could not fit in the buffer.
.TP
.B ENOMEM
The kernel could not allocate memory for the temporary buffer holding
the path.
.TP
.B EPERM
The process does not have the capability
.B CAP_SYS_ADMIN
required to look up cookie values.
.TP
.B ERANGE
The buffer was not large enough to hold the path of the directory entry.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 2.5.43.
.P
The
.B ENAMETOOLONG
error was added in Linux 2.5.70.
.SH NOTES
.BR lookup_dcookie ()
is a special-purpose system call, currently used only by the
.BR oprofile (1)
profiler.
It relies on a kernel driver to register cookies for directory entries.
.P
The path returned may be suffixed by the string " (deleted)" if the directory
entry has been removed.
.SH SEE ALSO
.BR oprofile (1)