[dpdk-dev] [RFC PATCH 1/2] ethdev: add capability to keep flow rules on restart

[Dmitry Kozlyuk <dkozlyuk@nvidia.com>]

Currently, it is not specified what happens to the flow rules when
the device is stopped, possibly reconfigured, then started.
If flow rules were kept, it can be convenient for application
developers, because they wouldn't need to save and restore them.
However, due to the number of flows and possible creation rate it is
impractical to save all flow rules in DPDK layer. This means that flow
rules persistence really depends on whether PMD and HW can implement it
efficiently. It is proposed for PMDs to advertise this capability
if supported using a new flag.

If the device is being reconfigured in a way that is incompatible with
existing flow rules, PMD is required to report an error.
This is mandatory, because flow API does not supply users with
capabilities, so this is the only way for a user to learn that
configuration is invalid. For example, if queue count changes and the
action of a flow rule specifies queues that are going away, the user
must update or remove the flow rule before removing the queues.

Signed-off-by: Dmitry Kozlyuk <dkozlyuk@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>
Acked-by: Ori Kam <orika@nvidia.com>
---
 doc/guides/prog_guide/rte_flow.rst | 9 +++++++++
 lib/ethdev/rte_ethdev.h            | 2 ++
 2 files changed, 11 insertions(+)

diff --git a/doc/guides/prog_guide/rte_flow.rst b/doc/guides/prog_guide/rte_flow.rst
index 2b42d5ec8c..0a03097a7c 100644
--- a/doc/guides/prog_guide/rte_flow.rst
+++ b/doc/guides/prog_guide/rte_flow.rst
@@ -87,6 +87,15 @@ To avoid resource leaks on the PMD side, handles must be explicitly
 destroyed by the application before releasing associated resources such as
 queues and ports.
 
+By default flow rules are implicitly destroyed when the device is stopped.
+If the device advertises ``RTE_DEV_CAPA_FLOW_RULE_KEEP``, flow rules persist
+across device stop and start with possible reconfiguration in between.
+Some configuration changes may be incompatible with existing flow rules,
+in this case ``rte_eth_dev_configure()`` or ``rte_eth_rx/tx_queue_setup()``
+will fail. At this point PMD developers are encouraged to log errors identical
+to the ones that would be emitted by ``rte_flow_create()`` if the new
+configuration was active.
+
 The following sections cover:
 
 - **Attributes** (represented by ``struct rte_flow_attr``): properties of a
diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
index d2b27c351f..1616bdf2dd 100644
--- a/lib/ethdev/rte_ethdev.h
+++ b/lib/ethdev/rte_ethdev.h
@@ -1448,6 +1448,8 @@ struct rte_eth_conf {
 #define RTE_ETH_DEV_CAPA_RUNTIME_RX_QUEUE_SETUP 0x00000001
 /** Device supports Tx queue setup after device started. */
 #define RTE_ETH_DEV_CAPA_RUNTIME_TX_QUEUE_SETUP 0x00000002
+/** Device keeps flow rules across restart and reconfiguration. */
+#define RTE_ETH_DEV_CAPA_FLOW_RULE_KEEP 0x00000004
 /**@}*/
 
 /*
-- 
2.25.1