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+# Egress mirroring support and ACL action capability check
+
+# Table of Contents
+
+#### Revision
+| Rev |  Date   |       Author       | Change Description |
+|:---:|:-------:|:------------------:|:------------------:|
+| 0.1 | 2019-05 |   Blyschak Stepan  | Initial Version    |
+
+## Motivation
+Not all ASICs support all actions on ingress, egress stages
+
+E.g.: Egress mirror action on ingress stage or vice versa might be not supported
+
+## Design
+
+## 1. Egress mirroring support
+
+SAI API has two mirror action types - SAI_ACL_ACTION_TYPE_MIRROR_INGRESS, SAI_ACL_ACTION_TYPE_MIRROR_EGRESS which can be set on ingress or egress table.
+So SONiC will not restrict setting egress mirror rule on ingress table or vice versa.
+To check wheter such combination is supported by the ASIC application should look into SWITCH_CAPABILITY table which is described in part 2 of this document.
+
+The proposed new schema:
+
+### ACL_RULE_TABLE
+```
+mirror_action = 1*255VCHAR                         ; refer to the mirror session (implicitly ingress for backward compatibility)
+mirror_ingress_action = 1*255VCHAR                 ; refer to the mirror session
+mirror_egress_action = 1*255VCHAR                  ; refer to the mirror session
+```
+
+e.g.:
+```
+{
+  "ACL_RULE": {
+        "EVERFLOW_INGRESS|RULE_1": {
+            "MIRROR_EGRESS_ACTION": "everflow0",
+            "PRIORITY": "9999",
+            "SRC_IP": "20.0.0.10/32"
+        }
+}
+```
+
+The above example shows setting an egress mirror action on ingress everflow table.
+
+mirror_action should be implicitly set to "ingress" by default to be backward compatible
+
+
+### orchagent
+
+- AclRuleMirror adds processing of new schema and convert to SAI_ACL_ACTION_TYPE_MIRROR_INGRESS/EGRESS based on action key;
+- By default mirror action is considered "ingress" to be backward compatible;
+
+### acl-loader
+
+- By default acl-loader with ```--session_name``` parameter will produce ingress mirror rule;
+- A new parameter ```--mirror_stage=ingress|egress``` will be added;
+
+e.g.:
+
+```
+admin@sonic:~$ acl-loader update incremental --session_name=everflow0 --mirror_stage=egress rules.json
+```
+
+## 2. ACL action capability check
+
+### orchagent
+
+AclOrch on initialization will query ACL stage capabilities and store them in internal map:
+
+| SAI attribute                                         |  Comment                                        |
+|:-----------------------------------------------------:|:-----------------------------------------------:|
+|SAI_SWITCH_ATTR_MAX_ACL_ACTION_COUNT                   | max acl action count                            |
+|SAI_SWITCH_ATTR_ACL_STAGE_INGRESS                      | list of action types supported on ingress stage |
+|SAI_SWITCH_ATTR_ACL_STAGE_EGRESS                       | list of action types supported on egress stage  |
+
+For those ACL entry attributes which have isenum == true set in sai_attr_metadata_t we will query supported list of actions using ``` sai_query_attribute_enum_values_capability ```
+
+E.g for SAI_ACL_ENTRY_ATTR_ACTION_PACKET_ACTION:
+
+```c++
+status = sai_query_attribute_enum_values_capability(gSwitchId,
+                                                   SAI_OBJECT_TYPE_SWITCH,
+                                                   SAI_ACL_ENTRY_ATTR_ACTION_PACKET_ACTION,
+                                                   &enum_values_capability);
+if (status != SAI_STATUS_SUCCESS)
+{
+    SWSS_LOG_THROW("sai_query_attribute_enum_values_capability failed");
+}
+```
+
+The above query will return a list of supported actions from ```sai_packet_action_t``` (DROP/FORWARD/COPY/TRAP etc.)
+
+**NOTE**: sai_query_attribute_enum_values_capability does not return values supported per stage
+
+**TODO**: sai_query_attribute_enum_values_capability not yet supported by libsairedis implementation
+
+#### aclorch.cpp
+
+```c++
+class AclOrch
+{
+public:
+  ...
+  // return true if action in attr is supported at stage otherwise return false
+  bool isActionSupported(acl_stage_type_t stage, sai_acl_entry_attr_t attr) const;
+  ...
+private:
+
+   // query SAI_SWITCH_ATTR_ACL_STAGE_INGRESS/SAI_SWITCH_ATTR_STAGE_EGRESS
+   // will be called from AclOrch::init();
+   void queryAclCapabilities();
+
+   std::map<sai_acl_stage_t, std::set<sai_acl_action_type_t>> m_aclStageCapabilities;
+   std::map<sai_acl_entry_attr_t, std::set<int32_t>> m_aclEnumActionCapabilities;
+...
+};
+```
+
+and in AclRule
+
+```c++
+class AclRule
+{
+public:
+  ...
+  // generic validation of ACL action based on m_aclStageCapabilities
+  // if some of sai_acl_entry_attr_t values in m_actions keys are enums (isenum == true)
+  // validate based on m_aclEnumActionCapabilities
+  virtual bool validateAddAction(string attr_name, string attr_value);
+  ...
+};
+```
+
+AclRule derivatives will call base class method ```AclRule::validateAddAction```, e.g. AclRuleMirror:
+
+```c++
+AclRuleMirror::validateAddAction(string attr_name, string attr_value)
+{
+  ... //
+  ... // validate
+
+  ... // fill in m_actions map
+
+  return AclRule::validateAddAction(attr_name, attr_value);
+}
+```
+
+### VS test
+
+Test case 1:
+
+VS test cases update to check for differnt combinations ingress/egress table and ingress/egress mirror rule creation
+
+### system level testing
+
+TBD
+
+### Switch capability table
+
+We will put ACL capabilities in state DB table:
+
+```
+SWITCH_CAPABILITY|switch
+```
+
+e.g:
+```
+127.0.0.1:6379[6]> hgetall "SWITCH_CAPABILITY|switch"
+1) "ACL_ACTIONS|INGRESS"
+2) "PACKET_ACTION,REDIRECT_ACTION,MIRROR_ACTION_INGRESS"
+3) "ACL_ACTIONS|EGRESS"
+4) "PACKET_ACTION,MIRROR_ACTION_EGRESS"
+...
+```
+
+For those action keys which are enums we will put queried supported enum values in DB
+```
+5) "ACL_ACTION|PACKET_ACTION"
+6) "DROP,FORWARD,COPY,TRAP"
+```
+
+Producer for ACL_RULE table like acl-loader will look at "ACL_ACTIONS|table-stage" to get a list of supported action keys.
+If key is in the list of supported, it will look if "ACL_ACTION|action-key" exists, if it doesn't exist we cannot validate action value (e.g value is not an enum but object like in redirect or mirror key), otherwise acl-loader gets a list of supported values and checks if value is in the list.
+
+#### NOTE
+
+To be consistent with SAI data type 'redirect:<param>' will be moved out from PACKET_ACTION key to own REDIRECT_ACTION key.
+Old config like ```"PACKET_ACTION": "redirect:Ethernet8"``` should still work for backward compatibility.
+
+##### ACL_RULE_TABLE
+```
+redirect_action = 1*255VCHAR                         ; refer to the redirect object
+```
+
+
+### libsairedis
+
+Implement SAI_ATTR_VALUE_TYPE_ACL_CAPABILITY deserialization as it is missing
+**DONE**
+
+### vslib
+
+Add support for SAI_SWITCH_ATTR_ACL_STAGE_INGRESS, SAI_SWITCH_ATTR_ACL_STAGE_EGRESS to VS.
+
+Two options:
+1. Return all actions as supported
+2. Return per VS simulating specific device. Currently there are MLNX and BRCM
+
+Second options is harder to maintain:
+1. every SAI (mlnx/brcm) update will require to check if list of supported actions were updated and update a VS library correspondingly and also update VS test.
+2. VS tests need to check which acl test cases to run for which vs simulating device
+
+So, we prefer to go with first option to make all actions returned as supported by VS.
+
+### VS test
+
+Check negative flow in case action is not supported.
+
+For ingress and egress tables:
+  - Set custom SAI_SWITCH_ATTR_ACL_STAGE_$STAGE attribute using setReadOnlyAttribute mechanism in VS test infrastructure and restart orchagent to make it reconstruct its capability map;
+  - Create ACL rule wich is not supported and verify no entry in ASIC DB;
+
+### system level testing
+
+TBD