mac80211: track assigned vifs in chanctx

This can be useful. Provides a more straghtforward
way to iterate over interfaces bound to a given
chanctx and allows tracking chanctx usage
explicitly.

The structure is protected by local->chanctx_mtx.
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/chan.c

@@ -276,6 +276,7 @@ ieee80211_new_chanctx(struct ieee80211_local *local,
 	if (!ctx)
 		return ERR_PTR(-ENOMEM);
 
+	INIT_LIST_HEAD(&ctx->assigned_vifs);
 	ctx->conf.def = *chandef;
 	ctx->conf.rx_chains_static = 1;
 	ctx->conf.rx_chains_dynamic = 1;
@@ -420,6 +421,7 @@ static int ieee80211_assign_vif_chanctx(struct ieee80211_sub_if_data *sdata,
 		curr_ctx->refcount--;
 		drv_unassign_vif_chanctx(local, sdata, curr_ctx);
 		conf = NULL;
+		list_del(&sdata->assigned_chanctx_list);
 	}
 
 	if (new_ctx) {
@@ -429,6 +431,8 @@ static int ieee80211_assign_vif_chanctx(struct ieee80211_sub_if_data *sdata,
 
 		new_ctx->refcount++;
 		conf = &new_ctx->conf;
+		list_add(&sdata->assigned_chanctx_list,
+			 &new_ctx->assigned_vifs);
 	}
 
 out:

net/mac80211/ieee80211_i.h

@@ -691,6 +691,8 @@ struct ieee80211_chanctx {
 	struct list_head list;
 	struct rcu_head rcu_head;
 
+	struct list_head assigned_vifs;
+
 	enum ieee80211_chanctx_mode mode;
 	int refcount;
 	bool driver_present;
@@ -756,6 +758,8 @@ struct ieee80211_sub_if_data {
 	bool csa_radar_required;
 	struct cfg80211_chan_def csa_chandef;
 
+	struct list_head assigned_chanctx_list; /* protected by chanctx_mtx */
+
 	/* context reservation -- protected with chanctx_mtx */
 	struct ieee80211_chanctx *reserved_chanctx;
 	struct cfg80211_chan_def reserved_chandef;

net/mac80211/iface.c

@@ -1291,6 +1291,7 @@ static void ieee80211_setup_sdata(struct ieee80211_sub_if_data *sdata,
 	INIT_WORK(&sdata->work, ieee80211_iface_work);
 	INIT_WORK(&sdata->recalc_smps, ieee80211_recalc_smps_work);
 	INIT_WORK(&sdata->csa_finalize_work, ieee80211_csa_finalize_work);
+	INIT_LIST_HEAD(&sdata->assigned_chanctx_list);
 
 	switch (type) {
 	case NL80211_IFTYPE_P2P_GO: