[PATCH v2] user: Mention file descriptor changes

[Chris Johns]

Hi,

Thank you for the update. I am not sure which branch this is for but it is OK
for the 5 branch.

Thanks
Chris

On 1/9/20 4:57 pm, Sebastian Huber wrote:
> ---
>  user/migration/v4_11-to-v5.rst | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/user/migration/v4_11-to-v5.rst b/user/migration/v4_11-to-v5.rst
> index d42744d..8016a63 100644
> --- a/user/migration/v4_11-to-v5.rst
> +++ b/user/migration/v4_11-to-v5.rst
> @@ -69,6 +69,23 @@ The directive :c:func:`rtems_clock_get` was removed.  See section
>  `Transition Advice for the Removed rtems_clock_get()` in the
>  `RTEMS Classic API Guide` for alternatives.
>  
> +File Descriptors
> +----------------
> +
> +In RTEMS 5.1, the list of free file descriptors has a LIFO ordering in contrast
> +to previous versions where it was a FIFO.  This means if an application
> +regularly opens and closes files (or sockets) it sees the whole range of file
> +descriptors.  The reason for this change was to increase the time before file
> +descriptors are reused to more likely catch a file descriptor use after close.
> +
> +This change may surface application issues.  If the configured file descriptor
> +maximum (``CONFIGURE_MAXIMUM_FILE_DESCRIPTORS``) is greater than the
> +``FD_SETSIZE`` defined by Newlib to 64, then calls to ``select()`` are undefined
> +behaviour and may corrupt the thread stack.  It is possible to define a custom
> +``FD_SETSIZE``.  The application must ensure that the custom ``FD_SETSIZE`` is
> +defined before ``<sys/select.h>`` is included in all modules used by the
> +application, for example via a global compiler command line define.
> +
>  Networking
>  ----------
>  
>