[PATCH requirements v4 5/7] net-features: Add n-tuple receive flow filters requirements

[Parav Pandit <parav@nvidia.com>]

Add virtio net device requirements for receive flow filters.

Signed-off-by: Parav Pandit <parav@nvidia.com>
---
changelog:
v3->v4:
- Addressed comments from Satananda, Heng, David
- removed context specific wording, replaced with destination
- added group create/delete examples and updated requirements
- added optional support to use cvq for flor filter commands
- added example of transporting flow filter commands over cvq
- made group size to be 16-bit
- added concept of 0->n max flow filter entries based on max count
- added concept of 0->n max flow group based on max count
- split field bitmask to separate command from other filter capabilities
- rewrote rx filter processing chain order with respect to existing
  filter commands and rss
- made flow_id flat across all groups
v1->v2:
- split setup and operations requirements
- added design goal
- worded requirements more precisely
v0->v1:
- fixed comments from Heng Li
- renamed receive flow steering to receive flow filters
- clarified byte offset in match criteria
---
 net-workstream/features-1.4.md | 151 +++++++++++++++++++++++++++++++++
 1 file changed, 151 insertions(+)

diff --git a/net-workstream/features-1.4.md b/net-workstream/features-1.4.md
index cb72442..78bb3d2 100644
--- a/net-workstream/features-1.4.md
+++ b/net-workstream/features-1.4.md
@@ -9,6 +9,7 @@ together is desired while updating the virtio net interface.
 1. Device counters visible to the driver
 2. Low latency tx and rx virtqueues for PCI transport
 3. Virtqueue notification coalescing re-arming support
+4  Virtqueue receive flow filters (RFF)
 
 # 3. Requirements
 ## 3.1 Device counters
@@ -183,3 +184,153 @@ struct vnet_rx_completion {
    notifications until the driver rearms the notifications of the virtqueue.
 2. When the driver rearms the notification of the virtqueue, the device
    to notify again if notification coalescing conditions are met.
+
+## 3.4 Virtqueue receive flow filters (RFF)
+0. Design goal:
+   To filter and/or to steer packet based on specific pattern match to a
+   specific destination to support application/networking stack driven receive
+   processing.
+1. Two use cases are: to support Linux netdev set_rxnfc() for ETHTOOL_SRXCLSRLINS
+   and to support netdev feature NETIF_F_NTUPLE aka ARFS.
+
+### 3.4.1 control path
+1. The number of flow filter operations/sec can range from 100k/sec to 1M/sec
+   or even more. Hence flow filter operations must be done over a queueing
+   interface using one or more queues.
+2. The device should be able to expose one or more supported flow filter queue
+   count and its start vq index to the driver.
+3. As each device may be operating for different performance characteristic,
+   start vq index and count may be different for each device. Secondly, it is
+   inefficient for device to provide flow filters capabilities via a config space
+   region. Hence, the device should be able to share these attributes using
+   dma interface, instead of transport registers.
+4. Since flow filters are enabled much later in the driver life cycle, driver
+   will likely create these queues when flow filters are enabled.
+5. Flow filter operations are often accelerated by device in a hardware. Ability
+   to handle them on a queue other than control vq is desired. This achieves near
+   zero modifications to existing implementations to add new operations on new
+   purpose built queues (similar to transmit and receive queue).
+   Therefore, when flow filter queues are supported, it is strongly recommended
+   to use it, when flow filter queues are not supported, if the device support
+   it using cvq, driver should be able to use over cvq.
+6. The filter masks are optional; the device should be able to expose if it
+   support filter masks.
+7. The driver may want to have priority among group of flow entries; to facilitate
+   the device support grouping flow filter entries by a notion of a flow group.
+   Each flow group defines priority in processing flow.
+8. The driver and group owner driver should be able to query supported device
+   limits for the receive flow filters.
+
+### 3.4.2 flow operations path
+1. The driver should be able to define a receive packet match criteria, an
+   action and a destination for a packet. For example, an ipv4 packet with a
+   multicast address to be steered to the receive vq 0. The second example is
+   ipv4, tcp packet matching a specified IP address and tcp port tuple to
+   be steered to receive vq 10.
+2. The match criteria should include exact tuple fields well-defined such as mac
+   address, IP addresses, tcp/udp ports, etc.
+3. The match criteria should also optionally include the field mask.
+5. Action includes (a) dropping or (b) forwarding the packet.
+6. Destination is a receive virtqueue index.
+7. Receive packet processing chain is:
+   a. filters programmed using cvq commands VIRTIO_NET_CTRL_RX,
+      VIRTIO_NET_CTRL_MAC and VIRTIO_NET_CTRL_VLAN.
+   b. filters programmed using RFF functiionality.
+   c. filters programmed using RSS VIRTIO_NET_CTRL_MQ_RSS_CONFIG command.
+   Whichever filtering and steering functionality is enabled, they are applied
+   in the above order.
+9. If multiple entries are programmed which has overlapping filtering attributes
+   for a received packet, the driver to define the location/priority of the entry.
+10. The filter entries are usually short in size of few tens of bytes,
+   for example IPv6 + TCP tuple would be 36 bytes, and ops/sec rate is
+   high, hence supplying fields inside the queue descriptor is preferred for
+   up to a certain fixed size, say 96 bytes.
+11. A flow filter entry consists of (a) match criteria, (b) action,
+    (c) destination and (d) a unique 32 bit flow id, all supplied by the
+    driver.
+12. The driver should be able to query and delete flow filter entry by the
+    the device by the flow id.
+
+### 3.4.3 interface example
+
+1. Flow filter capabilities to query using a DMA interface such as cvq
+using two different commands.
+
+```
+/* command 1 */
+struct flow_filter_capabilities {
+	le16 start_vq_index;
+	le16 num_flow_filter_vqs;
+	le16 max_flow_groups;
+	le16 max_group_priorities; /* max priorities of the group */
+	le32 max_flow_filters_per_group;
+	le32 max_flow_filters; /* max flow_id in add/del 
+				* is equal = max_flow_filters - 1.
+				*/
+	u8 max_priorities_per_group;
+};
+
+/* command 2 */
+struct flow_filter_fields_support_mask {
+	le64 supported_packet_field_mask_bmap[1];
+};
+
+```
+
+2. Group add/delete cvq commands:
+```
+
+struct virtio_net_rff_group_add {
+	le16 priority;
+	le16 group_id;
+};
+
+
+struct virtio_net_rff_group_delete {
+	le16 group_id;
+
+```
+
+3. Flow filter entry add/modify, delete over flow vq:
+
+```
+struct virtio_net_rff_add_modify {
+	u8 flow_op;
+	u8 padding;
+	u16 group_id;
+	le32 flow_id;
+	struct match_criteria mc;
+	struct destination dest;
+	struct action action;
+
+	struct match_criteria mask;	/* optional */
+};
+
+struct virtio_net_rff_delete {
+	u8 flow_op;
+	u8 padding[3];
+	le32 flow_id;
+};
+
+```
+
+4. Flow filter commands over cvq:
+
+```
+
+struct virtio_net_rff_cmd {
+	u8 class; /* RFF class */
+	u8 commands; /* RFF cmd = A */
+	u8 command-specific-data[]; /* contains struct virtio_net_rff_add_modify or 
+				     * struct virtio_net_rff_delete
+                                     */
+};
+
+```
+
+### 3.4.4 For incremental future
+a. Driver should be able to specify a specific packet byte offset, number
+   of bytes and mask as math criteria.
+b. Support RSS context, in addition to a specific RQ.
+c. If/when virtio switch object is implemented, support ingress/egress flow
+   filters at the switch port level.
-- 
2.26.2