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authorSebastian Huber <sebastian.huber@embedded-brains.de>2020-09-01 07:03:49 +0200
committerSebastian Huber <sebastian.huber@embedded-brains.de>2020-09-02 07:17:55 +0200
commitbd8185a7dda9b8fc936a4f85b19d67f13d7a393c (patch)
tree7b33dee15b20525f1f5c4a496b1e023c6bed51da /user/migration/v4_11-to-v5.rst
parent415b072babcf230af7fde2809cff1042db3ef48a (diff)
downloadrtems-docs-bd8185a7dda9b8fc936a4f85b19d67f13d7a393c.tar.bz2
user: Mention file descriptor changes
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diff --git a/user/migration/v4_11-to-v5.rst b/user/migration/v4_11-to-v5.rst
index d42744d..bde84c2 100644
--- a/user/migration/v4_11-to-v5.rst
+++ b/user/migration/v4_11-to-v5.rst
@@ -69,6 +69,25 @@ 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. In particular, ``FD_SET()`` may
+result in an out of bounds access. 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. This
+applies also to all third-party libraries used by the application.
+
Networking
----------