[PATCH v2 1/3] mac80211: add ieee80211_tx_peek API

[Jose Ignacio Tornos Martinez <jtornosm@redhat.com>]

Add ieee80211_tx_peek() to allow drivers to inspect the next frame
in a TXQ without removing it.

Drivers implementing custom wake_tx_queue operations may need to
determine which hardware TX ring to use before dequeuing a packet,
using properties like the skb hash or queue mapping that are only
available from the skb itself.

The function checks pending fragments first, then iterates through
all fair-queue flows (new_flows and old_flows) to find the first
queued frame, matching the iteration behavior of fq_tin_dequeue.
It also pre-caches the skb hash via skb_get_hash() so that
hash-based ring selectors see a stable value through the subsequent
dequeue and TX path.

Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>
---
New in v2

 include/net/mac80211.h | 20 ++++++++++++++++++++
 net/mac80211/tx.c      | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 4f95da023746..9289b8dca972 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -7742,6 +7742,26 @@ void ieee80211_unreserve_tid(struct ieee80211_sta *sta, u8 tid);
 struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
 				     struct ieee80211_txq *txq);
 
+/**
+ * ieee80211_tx_peek - peek at the next packet in a software tx queue
+ *
+ * @hw: pointer as obtained from ieee80211_alloc_hw()
+ * @txq: pointer obtained from station or virtual interface, or from
+ *	ieee80211_next_txq()
+ *
+ * Return: the next skb without dequeuing it, or %NULL if the queue is empty.
+ * The returned pointer is const — the caller must not modify or free the skb.
+ * The skb remains queued and will be returned by a subsequent
+ * ieee80211_tx_dequeue() call.
+ *
+ * This is useful for drivers that need to inspect the next frame (e.g. to
+ * determine the target TX ring) before deciding whether to dequeue.
+ *
+ * Must be called in the same context as ieee80211_tx_dequeue().
+ */
+const struct sk_buff *ieee80211_tx_peek(struct ieee80211_hw *hw,
+					struct ieee80211_txq *txq);
+
 /**
  * ieee80211_tx_dequeue_ni - dequeue a packet from a software tx queue
  * (in process context)
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index c13b209fad47..91bfd8ef9428 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -3857,6 +3857,45 @@ static bool ieee80211_xmit_fast(struct ieee80211_sub_if_data *sdata,
 	return true;
 }
 
+const struct sk_buff *ieee80211_tx_peek(struct ieee80211_hw *hw,
+					struct ieee80211_txq *txq)
+{
+	struct txq_info *txqi = container_of(txq, struct txq_info, txq);
+	struct ieee80211_local *local = hw_to_local(hw);
+	struct fq_tin *tin = &txqi->tin;
+	struct fq *fq = &local->fq;
+	struct sk_buff *skb = NULL;
+	struct fq_flow *flow;
+
+	WARN_ON_ONCE(softirq_count() == 0);
+
+	spin_lock_bh(&fq->lock);
+
+	skb = skb_peek(&txqi->frags);
+	if (skb)
+		goto out;
+
+	list_for_each_entry(flow, &tin->new_flows, flowchain) {
+		skb = skb_peek(&flow->queue);
+		if (skb)
+			goto out;
+	}
+
+	list_for_each_entry(flow, &tin->old_flows, flowchain) {
+		skb = skb_peek(&flow->queue);
+		if (skb)
+			goto out;
+	}
+
+out:
+	if (skb)
+		skb_get_hash(skb);
+
+	spin_unlock_bh(&fq->lock);
+	return skb;
+}
+EXPORT_SYMBOL_GPL(ieee80211_tx_peek);
+
 struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
 				     struct ieee80211_txq *txq)
 {
-- 
2.54.0