From edd025ca088719770c77a27266bf03f2f39ce83d Mon Sep 17 00:00:00 2001 From: Edward Cree Date: Mon, 27 Mar 2023 11:36:03 +0100 Subject: [PATCH] sfc: document TC-to-EF100-MAE action translation concepts Includes an explanation of the lifetime of the 'cursor' action-set `act`. Signed-off-by: Edward Cree Reviewed-by: Simon Horman Signed-off-by: David S. Miller --- drivers/net/ethernet/sfc/tc.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-) diff --git a/drivers/net/ethernet/sfc/tc.c b/drivers/net/ethernet/sfc/tc.c index 2b07bb2fd735..34c1ff87ba5e 100644 --- a/drivers/net/ethernet/sfc/tc.c +++ b/drivers/net/ethernet/sfc/tc.c @@ -66,7 +66,7 @@ static const struct rhashtable_params efx_tc_match_action_ht_params = { static void efx_tc_free_action_set(struct efx_nic *efx, struct efx_tc_action_set *act, bool in_hw) { - /* Failure paths calling this on the 'running action' set in_hw=false, + /* Failure paths calling this on the 'cursor' action set in_hw=false, * because if the alloc had succeeded we'd've put it in acts.list and * not still have it in act. */ @@ -407,6 +407,30 @@ static int efx_tc_flower_replace(struct efx_nic *efx, goto release; } + /** + * DOC: TC action translation + * + * Actions in TC are sequential and cumulative, with delivery actions + * potentially anywhere in the order. The EF100 MAE, however, takes + * an 'action set list' consisting of 'action sets', each of which is + * applied to the _original_ packet, and consists of a set of optional + * actions in a fixed order with delivery at the end. + * To translate between these two models, we maintain a 'cursor', @act, + * which describes the cumulative effect of all the packet-mutating + * actions encountered so far; on handling a delivery (mirred or drop) + * action, once the action-set has been inserted into hardware, we + * append @act to the action-set list (@rule->acts); if this is a pipe + * action (mirred mirror) we then allocate a new @act with a copy of + * the cursor state _before_ the delivery action, otherwise we set @act + * to %NULL. + * This ensures that every allocated action-set is either attached to + * @rule->acts or pointed to by @act (and never both), and that only + * those action-sets in @rule->acts exist in hardware. Consequently, + * in the failure path, @act only needs to be freed in memory, whereas + * for @rule->acts we remove each action-set from hardware before + * freeing it (efx_tc_free_action_set_list()), even if the action-set + * list itself is not in hardware. + */ flow_action_for_each(i, fa, &fr->action) { struct efx_tc_action_set save; u16 tci;