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       lookup_dcookie - return a directory entry’s path


       int lookup_dcookie(u64 cookie, char *buffer, size_t len);


       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.


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


       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.

              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.


       Available since Linux 2.5.43.  The ENAMETOOLONG error return was  added
       in 2.5.70.


       lookup_dcookie() is Linux-specific.


       lookup_dcookie()  is a special-purpose system call, currently used only
       by the oprofile 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.


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