[PATCH v4] landlock: Clarify documentation for the LANDLOCK_ACCESS_FS_REFER right

[Mickaël Salaün]

On 25/02/2023 00:00, Alex Colomar wrote:
> Hi Günther,
> 
> On 2/21/23 17:52, Günther Noack wrote:
> [...]
> 
> Sorry for taking so much time in looking into this!
> 
>> + *
>> + *   * The reparented file may not gain more access rights in the destination
>> + *     directory than it previously had in the source directory.  If this is
>> + *     attempted, the operation results in an ``EXDEV`` error.
>> + *
>> + *   * When linking or renaming, the ``LANDLOCK_ACCESS_FS_MAKE_*`` right for the
>> + *     respective file type must be granted for the destination directory.
>> + *     Otherwise, the operation results in an ``EACCES`` error.
>> + *
>> + *   * When renaming, the ``LANDLOCK_ACCESS_FS_REMOVE_*`` right for the
>> + *     respective file type must be granted for the source directory.  Otherwise,
>> + *     the operation results in an ``EACCES`` error.
>> + *
>> + *   If multiple requirements are not met, the ``EACCES`` error code takes
>> + *   precedence over ``EXDEV``.
> 
> Is this something worth guaranteeing, or just an implementation detail
> that may easily change?

There is a deliberate effort to keep this error priority to be able to 
know if a rename or link action can be replaced with a file copy, which 
is useful e.g., for `mv`.