doc: announce deprecation of max constants as array size

Adding the deprecation notice as reminder for next ABI breakage release
(20.11).
This one time breakage is required to be able to extend enum/define
without breaking ABI.

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: David Marchand <david.marchand@redhat.com>

diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
index dfcca87..99d8156 100644 (file)
--- a/doc/guides/rel_notes/deprecation.rst
+++ b/doc/guides/rel_notes/deprecation.rst
@@ -38,6 +38,20 @@ Deprecation Notices
   remove it from the externally visible ABI and allow it to be updated in the
   future.
 
+* lib: will fix extending some enum/define breaking the ABI. There are multiple
+  samples in DPDK that enum/define terminated with a ``.*MAX.*`` value which is
+  used by iterators, and arrays holding these values are sized with this
+  ``.*MAX.*`` value. So extending this enum/define increases the ``.*MAX.*``
+  value which increases the size of the array and depending on how/where the
+  array is used this may break the ABI.
+  ``RTE_ETH_FLOW_MAX`` is one sample of the mentioned case, adding a new flow
+  type will break the ABI because of ``flex_mask[RTE_ETH_FLOW_MAX]`` array
+  usage in following public struct hierarchy:
+  ``rte_eth_fdir_flex_conf -> rte_fdir_conf -> rte_eth_conf (in the middle)``.
+  Need to identify this kind of usages and fix in 20.11, otherwise this blocks
+  us extending existing enum/define.
+  One solution can be using a fixed size array instead of ``.*MAX.*`` value.
+
 * dpaa2: removal of ``rte_dpaa2_memsegs`` structure which has been replaced
   by a pa-va search library. This structure was earlier being used for holding
   memory segments used by dpaa2 driver for faster pa->va translation. This