Linux cli command lookup_dcookie

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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(SYS_lookup_dcookie, uint64_t cookie, char *buffer,
 size_t len);

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 special-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.

SEE ALSO

oprofile(1)

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