doc: announce ABI change for ring library

Document proposed changes for the rings code in the next release.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>

doc/guides/rel_notes/deprecation.rst

@@ -8,6 +8,26 @@ API and ABI deprecation notices are to be posted here.
 Deprecation Notices
 -------------------
 
+* ring: Changes are planned to rte_ring APIs in release 17.05. Proposed
+  changes include:
+
+    - Removing build time options for the ring:
+      CONFIG_RTE_RING_SPLIT_PROD_CONS
+      CONFIG_RTE_RING_PAUSE_REP_COUNT
+    - Adding an additional parameter to enqueue functions to return the
+      amount of free space in the ring
+    - Adding an additional parameter to dequeue functions to return the
+      number of remaining elements in the ring
+    - Removing direct support for watermarks in the rings, since the
+      additional return value from the enqueue function makes it
+      unneeded
+    - Adjusting the return values of the bulk() enq/deq functions to
+      make them consistent with the burst() equivalents. [Note, parameter
+      to these functions are changing too, per points above, so compiler
+      will flag them as needing update in legacy code]
+    - Updates to some library functions e.g. rte_ring_get_memsize() to
+      allow for variably-sized ring elements.
+
 * igb_uio: iomem mapping and sysfs files created for iomem and ioport in
   igb_uio will be removed, because we are able to detect these from what Linux
   has exposed, like the way we have done with uio-pci-generic. This change