[v5,06/78] xarray: Change definition of sibling entries

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Fri, Dec 15, 2017 at 02:03:38PM -0800, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@microsoft.com>
> 
> Instead of storing a pointer to the slot containing the canonical entry,
> store the offset of the slot.  Produces slightly more efficient code
> (~300 bytes) and simplifies the implementation.
> 
> Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
> ---
>  include/linux/xarray.h | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  lib/radix-tree.c       | 65 +++++++++++----------------------------
>  2 files changed, 100 insertions(+), 47 deletions(-)
> 
> diff --git a/include/linux/xarray.h b/include/linux/xarray.h
> index 49fffc354431..f175350560fd 100644
> --- a/include/linux/xarray.h
> +++ b/include/linux/xarray.h
> @@ -49,6 +49,17 @@ static inline bool xa_is_value(const void *entry)
>  	return (unsigned long)entry & 1;
>  }
>  
> +/**
> + * xa_is_internal() - Is the entry an internal entry?
> + * @entry: Entry retrieved from the XArray
> + *
> + * Return: %true if the entry is an internal entry.
> + */

What does it mean "internal entry"? Is it just a term for non-value and
non-data pointer entry? Do we allow anybody besides xarray implementation to
use internal entires?

Do we have it documented?