mac80211: introduce channel context skeleton code

Channel context are the foundation for multi-channel
operation. They are are immutable and are re-created
(or re-used if other interfaces are bound to a certain
channel and a compatible channel type) on channel
switching.

This is an initial implementation and more features
will come in separate patches.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
[some changes including RCU protection]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

3 files changed, 185 insertions, 0 deletions

diff --git a/net/mac80211/chan.c b/net/mac80211/chan.c
index 0bfc914ddd15..4ae94860a161 100644
--- a/net/mac80211/chan.c
+++ b/net/mac80211/chan.c
@@ -168,3 +168,150 @@ bool ieee80211_set_channel_type(struct ieee80211_local *local,
         return true;
 
 }
+
+static struct ieee80211_chanctx *
+ieee80211_find_chanctx(struct ieee80211_local *local,
+                       struct ieee80211_channel *channel,
+                       enum nl80211_channel_type channel_type,
+                       enum ieee80211_chanctx_mode mode)
+{
+        struct ieee80211_chanctx *ctx;
+
+        lockdep_assert_held(&local->chanctx_mtx);
+
+        if (mode == IEEE80211_CHANCTX_EXCLUSIVE)
+                return NULL;
+        if (WARN_ON(!channel))
+                return NULL;
+
+        list_for_each_entry(ctx, &local->chanctx_list, list) {
+                if (ctx->mode == IEEE80211_CHANCTX_EXCLUSIVE)
+                        continue;
+                if (ctx->conf.channel != channel)
+                        continue;
+                if (ctx->conf.channel_type != channel_type)
+                        continue;
+
+                return ctx;
+        }
+
+        return NULL;
+}
+
+static struct ieee80211_chanctx *
+ieee80211_new_chanctx(struct ieee80211_local *local,
+                      struct ieee80211_channel *channel,
+                      enum nl80211_channel_type channel_type,
+                      enum ieee80211_chanctx_mode mode)
+{
+        struct ieee80211_chanctx *ctx;
+
+        lockdep_assert_held(&local->chanctx_mtx);
+
+        ctx = kzalloc(sizeof(*ctx) + local->hw.chanctx_data_size, GFP_KERNEL);
+        if (!ctx)
+                return ERR_PTR(-ENOMEM);
+
+        ctx->conf.channel = channel;
+        ctx->conf.channel_type = channel_type;
+        ctx->mode = mode;
+
+        list_add(&ctx->list, &local->chanctx_list);
+
+        return ctx;
+}
+
+static void ieee80211_free_chanctx(struct ieee80211_local *local,
+                                   struct ieee80211_chanctx *ctx)
+{
+        lockdep_assert_held(&local->chanctx_mtx);
+
+        WARN_ON_ONCE(ctx->refcount != 0);
+
+        list_del(&ctx->list);
+        kfree_rcu(ctx, rcu_head);
+}
+
+static int ieee80211_assign_vif_chanctx(struct ieee80211_sub_if_data *sdata,
+                                        struct ieee80211_chanctx *ctx)
+{
+        struct ieee80211_local *local __maybe_unused = sdata->local;
+
+        lockdep_assert_held(&local->chanctx_mtx);
+
+        rcu_assign_pointer(sdata->vif.chanctx_conf, &ctx->conf);
+        ctx->refcount++;
+
+        return 0;
+}
+
+static void ieee80211_unassign_vif_chanctx(struct ieee80211_sub_if_data *sdata,
+                                           struct ieee80211_chanctx *ctx)
+{
+        struct ieee80211_local *local __maybe_unused = sdata->local;
+
+        lockdep_assert_held(&local->chanctx_mtx);
+
+        ctx->refcount--;
+        rcu_assign_pointer(sdata->vif.chanctx_conf, NULL);
+}
+
+static void __ieee80211_vif_release_channel(struct ieee80211_sub_if_data *sdata)
+{
+        struct ieee80211_local *local = sdata->local;
+        struct ieee80211_chanctx_conf *conf;
+        struct ieee80211_chanctx *ctx;
+
+        lockdep_assert_held(&local->chanctx_mtx);
+
+        conf = rcu_dereference_protected(sdata->vif.chanctx_conf,
+                                         lockdep_is_held(&local->chanctx_mtx));
+        if (!conf)
+                return;
+
+        ctx = container_of(conf, struct ieee80211_chanctx, conf);
+
+        ieee80211_unassign_vif_chanctx(sdata, ctx);
+        if (ctx->refcount == 0)
+                ieee80211_free_chanctx(local, ctx);
+}
+
+int ieee80211_vif_use_channel(struct ieee80211_sub_if_data *sdata,
+                              struct ieee80211_channel *channel,
+                              enum nl80211_channel_type channel_type,
+                              enum ieee80211_chanctx_mode mode)
+{
+        struct ieee80211_local *local = sdata->local;
+        struct ieee80211_chanctx *ctx;
+        int ret;
+
+        mutex_lock(&local->chanctx_mtx);
+        __ieee80211_vif_release_channel(sdata);
+
+        ctx = ieee80211_find_chanctx(local, channel, channel_type, mode);
+        if (!ctx)
+                ctx = ieee80211_new_chanctx(local, channel, channel_type, mode);
+        if (IS_ERR(ctx)) {
+                ret = PTR_ERR(ctx);
+                goto out;
+        }
+
+        ret = ieee80211_assign_vif_chanctx(sdata, ctx);
+        if (ret) {
+                /* if assign fails refcount stays the same */
+                if (ctx->refcount == 0)
+                        ieee80211_free_chanctx(local, ctx);
+                goto out;
+        }
+
+ out:
+        mutex_unlock(&local->chanctx_mtx);
+        return ret;
+}
+
+void ieee80211_vif_release_channel(struct ieee80211_sub_if_data *sdata)
+{
+        mutex_lock(&sdata->local->chanctx_mtx);
+        __ieee80211_vif_release_channel(sdata);
+        mutex_unlock(&sdata->local->chanctx_mtx);
+}
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 8c804550465b..9a058e58d53e 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -658,6 +658,30 @@ enum ieee80211_sdata_state_bits {
         SDATA_STATE_OFFCHANNEL,
 };
 
+/**
+ * enum ieee80211_chanctx_mode - channel context configuration mode
+ *
+ * @IEEE80211_CHANCTX_SHARED: channel context may be used by
+ *      multiple interfaces
+ * @IEEE80211_CHANCTX_EXCLUSIVE: channel context can be used
+ *      only by a single interface. This can be used for example for
+ *      non-fixed channel IBSS.
+ */
+enum ieee80211_chanctx_mode {
+        IEEE80211_CHANCTX_SHARED,
+        IEEE80211_CHANCTX_EXCLUSIVE
+};
+
+struct ieee80211_chanctx {
+        struct list_head list;
+        struct rcu_head rcu_head;
+
+        enum ieee80211_chanctx_mode mode;
+        int refcount;
+
+        struct ieee80211_chanctx_conf conf;
+};
+
 struct ieee80211_sub_if_data {
         struct list_head list;
 
@@ -987,6 +1011,10 @@ struct ieee80211_local {
         struct ieee80211_channel *tmp_channel;
         enum nl80211_channel_type tmp_channel_type;
 
+        /* channel contexts */
+        struct list_head chanctx_list;
+        struct mutex chanctx_mtx;
+
         /* SNMP counters */
         /* dot11CountersTable */
         u32 dot11TransmittedFragmentCount;
@@ -1510,6 +1538,13 @@ bool ieee80211_set_channel_type(struct ieee80211_local *local,
 enum nl80211_channel_type
 ieee80211_ht_oper_to_channel_type(struct ieee80211_ht_operation *ht_oper);
 
+int __must_check
+ieee80211_vif_use_channel(struct ieee80211_sub_if_data *sdata,
+                          struct ieee80211_channel *channel,
+                          enum nl80211_channel_type channel_type,
+                          enum ieee80211_chanctx_mode mode);
+void ieee80211_vif_release_channel(struct ieee80211_sub_if_data *sdata);
+
 #ifdef CONFIG_MAC80211_NOINLINE
 #define debug_noinline noinline
 #else
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index c80c4490351c..9be3ef1d2e86 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -626,6 +626,9 @@ struct ieee80211_hw *ieee80211_alloc_hw(size_t priv_data_len,
         spin_lock_init(&local->filter_lock);
         spin_lock_init(&local->queue_stop_reason_lock);
 
+        INIT_LIST_HEAD(&local->chanctx_list);
+        mutex_init(&local->chanctx_mtx);
+
         /*
          * The rx_skb_queue is only accessed from tasklets,
          * but other SKB queues are used from within IRQ