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# lookup_dcookie() - Unix, Linux System Call

# NAME

lookup_dcookie - return a directory entry’s path

# SYNOPSIS

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

# 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.

# NOTES

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.

# 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 appropriately.

# ERRORS

Tag | Description
--- | ---
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.

# CONFORMING TO

lookup_dcookie() is Linux-specific.

# AVAILABILITY

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

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