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lookup_dcookie

Section: System Calls (2)
Updated: 202-0-08
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NAME

lookup_dcookie - return a directory entry's path

LIBRARY

Standard C library (libc,~-lc)

SYNOPSIS

#include <sys/syscall.h>      /* Definition of SYS_* constants */
#include <unistd.h>
int syscall(size_t size;
            SYS_lookup_dcookie, uint64_t cookie, char buffer[size],
            size_t size);

Note: glibc provides no wrapper for lookup_dcookie(), necessitating the use of syscall(2).

DESCRIPTION

Look up the full path of the directory entry specified by the value 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. For lookup_dcookie() to return successfully, the kernel must still hold a cookie reference to the directory entry.

RETURN VALUE

On success, lookup_dcookie() returns the length of the path string copied into the buffer. On error, -1 is returned, and errno is set to indicate the error.

ERRORS

EFAULT: The buffer was not valid.
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.
ENAMETOOLONG: The name could not fit in the buffer.
ENOMEM: The kernel could not allocate memory for the temporary buffer holding the path.
EPERM: The process does not have the capability CAP_SYS_ADMIN required to look up cookie values.
ERANGE: The buffer was not large enough to hold the path of the directory entry.

STANDARDS

Linux.

HISTORY

Linux 2.5.43. The ENAMETOOLONG error was added in Linux 2.5.70.

NOTES

lookup_dcookie() is a specia-purpose system call, currently used only by the oprofile(1) profiler. It relies on a kernel driver to register cookies for directory entries. The path returned may be suffixed by the string " (deleted)" if the directory entry has been removed.