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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.


       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.


       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.


       lookup_dcookie() is Linux-specific.


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