[PATCH RFC v2] mac80211: debugfs option to force TX status frames

[Julius Niedworok]

At Technical University of Munich we use MAC 802.11 TX status frames to
perform several measurements in MAC 802.11 setups.

With ath based drivers this was possible until commit d94a461d7a7df6
("ath9k: use ieee80211_tx_status_noskb where possible") as the driver
ignored the IEEE80211_TX_CTL_REQ_TX_STATUS flag and always delivered
tx_status frames. Since that commit, this behavior was changed and the
driver now adheres to IEEE80211_TX_CTL_REQ_TX_STATUS.

Due to performance reasons, IEEE80211_TX_CTL_REQ_TX_STATUS is not set for
data frames from interfaces in managed mode. Hence, frames that are sent
from a managed mode interface do never deliver tx_status frames. This
remains true even if a monitor mode interface (the measurement interface)
is added to the same ieee80211 physical device. Thus, there is no
possibility for receiving tx_status frames for frames sent on an interface
in managed mode, if the driver adheres to IEEE80211_TX_CTL_REQ_TX_STATUS.

In order to force delivery of tx_status frames for research and debugging
purposes, implement a debugfs option force_tx_status for ieee80211 physical
devices. When this option is set for a physical device,
IEEE80211_TX_CTL_REQ_TX_STATUS is enabled in all packets sent from that
device. This option can be set via
/sys/kernel/debug/ieee80211/<dev>/force_tx_status. The default is disabled.

Co-developed-by: Charlie Groh <ga58taw@xxxxxxxx>
Signed-off-by: Charlie Groh <ga58taw@xxxxxxxx>
Signed-off-by: Julius Niedworok <julius.n@xxxxxxx>
---
 net/mac80211/debugfs.c     | 53 ++++++++++++++++++++++++++++++++++++++++++++++
 net/mac80211/ieee80211_i.h |  1 +
 net/mac80211/tx.c          | 10 +++++++++
 3 files changed, 64 insertions(+)

diff --git a/net/mac80211/debugfs.c b/net/mac80211/debugfs.c
index 3fe541e..074b5d1 100644
--- a/net/mac80211/debugfs.c
+++ b/net/mac80211/debugfs.c
@@ -150,6 +150,58 @@ static const struct file_operations aqm_ops = {
 	.llseek = default_llseek,
 };
 
+static ssize_t force_tx_status_read(struct file *file,
+				    char __user *user_buf,
+			size_t count,
+			loff_t *ppos)
+{
+	struct ieee80211_local *local = file->private_data;
+	char buf[3];
+	int len = 0;
+
+	len = scnprintf(buf, sizeof(buf), "%d\n", (int)local->force_tx_status);
+
+	return simple_read_from_buffer(user_buf, count, ppos,
+				       buf, len);
+}
+
+static ssize_t force_tx_status_write(struct file *file,
+				     const char __user *user_buf,
+			 size_t count,
+			 loff_t *ppos)
+{
+	struct ieee80211_local *local = file->private_data;
+	char buf[3];
+	size_t len;
+
+	if (count > sizeof(buf))
+		return -EINVAL;
+
+	if (copy_from_user(buf, user_buf, count))
+		return -EFAULT;
+
+	buf[sizeof(buf) - 1] = '\0';
+	len = strlen(buf);
+	if (len > 0 && buf[len - 1] == '\n')
+		buf[len - 1] = 0;
+
+	if (buf[0] == '0' && buf[1] == '\0')
+		local->force_tx_status = 0;
+	else if (buf[0] == '1' && buf[1] == '\0')
+		local->force_tx_status = 1;
+	else
+		return -EINVAL;
+
+	return count;
+}
+
+static const struct file_operations force_tx_status_ops = {
+	.write = force_tx_status_write,
+	.read = force_tx_status_read,
+	.open = simple_open,
+	.llseek = default_llseek,
+};
+
 #ifdef CONFIG_PM
 static ssize_t reset_write(struct file *file, const char __user *user_buf,
 			   size_t count, loff_t *ppos)
@@ -379,6 +431,7 @@ void debugfs_hw_add(struct ieee80211_local *local)
 	DEBUGFS_ADD(hwflags);
 	DEBUGFS_ADD(user_power);
 	DEBUGFS_ADD(power);
+	DEBUGFS_ADD_MODE(force_tx_status, 0600);
 
 	if (local->ops->wake_tx_queue)
 		DEBUGFS_ADD_MODE(aqm, 0600);
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 7dfb4e2..3339b5d 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -1367,6 +1367,7 @@ struct ieee80211_local {
 		struct dentry *rcdir;
 		struct dentry *keys;
 	} debugfs;
+	bool force_tx_status;
 #endif
 
 	/*
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 928f13a..717fa71 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -2463,6 +2463,11 @@ static struct sk_buff *ieee80211_build_hdr(struct ieee80211_sub_if_data *sdata,
 	if (IS_ERR(sta))
 		sta = NULL;
 
+#ifdef CONFIG_MAC80211_DEBUGFS
+		if (local->force_tx_status)
+			info_flags |= IEEE80211_TX_CTL_REQ_TX_STATUS;
+#endif
+
 	/* convert Ethernet header to proper 802.11 header (based on
 	 * operation mode) */
 	ethertype = (skb->data[12] << 8) | skb->data[13];
@@ -3468,6 +3473,11 @@ static bool ieee80211_xmit_fast(struct ieee80211_sub_if_data *sdata,
 		      (tid_tx ? IEEE80211_TX_CTL_AMPDU : 0);
 	info->control.flags = IEEE80211_TX_CTRL_FAST_XMIT;
 
+#ifdef CONFIG_MAC80211_DEBUGFS
+		if (local->force_tx_status)
+			info->flags |= IEEE80211_TX_CTL_REQ_TX_STATUS;
+#endif
+
 	if (hdr->frame_control & cpu_to_le16(IEEE80211_STYPE_QOS_DATA)) {
 		tid = skb->priority & IEEE80211_QOS_CTL_TAG1D_MASK;
 		*ieee80211_get_qos_ctl(hdr) = tid;
-- 
2.10.1 (Apple Git-78)