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From:   Julius Niedworok <julius.n@gmx.net>
To:     linux-wireless@vger.kernel.org
Cc:     julius.n@gmx.net, ga58taw@mytum.de, david@redhat.com,
        nc@net.in.tum.de, Johannes Berg <johannes@sipsolutions.net>,
        "David S. Miller" <davem@davemloft.net>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v3] mac80211: debugfs option to force TX status frames
Date:   Thu, 28 Mar 2019 21:01:06 +0100
Message-Id: <20190328200108.98981-1-julius.n@gmx.net>
In-Reply-To: <e20962001ee10a0f90f8e2f1f8baafcf3b70e9dd.camel@sipsolutions.net>
References: <e20962001ee10a0f90f8e2f1f8baafcf3b70e9dd.camel@sipsolutions.net>
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Sender: linux-kernel-owner@vger.kernel.org
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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 physica=
l
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@mytum.de>
Signed-off-by: Charlie Groh <ga58taw@mytum.de>
Signed-off-by: Julius Niedworok <julius.n@gmx.net>
=2D--
 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 2d43bc1..da8f27c 100644
=2D-- a/net/mac80211/debugfs.c
+++ b/net/mac80211/debugfs.c
@@ -150,6 +150,58 @@ static const struct file_operations aqm_ops =3D {
 	.llseek =3D 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 =3D file->private_data;
+	char buf[3];
+	int len =3D 0;
+
+	len =3D 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 =3D 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] =3D '\0';
+	len =3D strlen(buf);
+	if (len > 0 && buf[len - 1] =3D=3D '\n')
+		buf[len - 1] =3D 0;
+
+	if (buf[0] =3D=3D '0' && buf[1] =3D=3D '\0')
+		local->force_tx_status =3D 0;
+	else if (buf[0] =3D=3D '1' && buf[1] =3D=3D '\0')
+		local->force_tx_status =3D 1;
+	else
+		return -EINVAL;
+
+	return count;
+}
+
+static const struct file_operations force_tx_status_ops =3D {
+	.write =3D force_tx_status_write,
+	.read =3D force_tx_status_read,
+	.open =3D simple_open,
+	.llseek =3D default_llseek,
+};
+
 #ifdef CONFIG_PM
 static ssize_t reset_write(struct file *file, const char __user *user_buf=
,
 			   size_t count, loff_t *ppos)
@@ -382,6 +434,7 @@ 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 e170f98..28ac87c 100644
=2D-- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -1384,6 +1384,7 @@ 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 8a49a74..a39ce49 100644
=2D-- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -2470,6 +2470,11 @@ static struct sk_buff *ieee80211_build_hdr(struct i=
eee80211_sub_if_data *sdata,
 	if (IS_ERR(sta))
 		sta =3D NULL;

+#ifdef CONFIG_MAC80211_DEBUGFS
+	if (local->force_tx_status)
+		info_flags |=3D IEEE80211_TX_CTL_REQ_TX_STATUS;
+#endif
+
 	/* convert Ethernet header to proper 802.11 header (based on
 	 * operation mode) */
 	ethertype =3D (skb->data[12] << 8) | skb->data[13];
@@ -3475,6 +3480,11 @@ static bool ieee80211_xmit_fast(struct ieee80211_su=
b_if_data *sdata,
 		      (tid_tx ? IEEE80211_TX_CTL_AMPDU : 0);
 	info->control.flags =3D IEEE80211_TX_CTRL_FAST_XMIT;

+#ifdef CONFIG_MAC80211_DEBUGFS
+	if (local->force_tx_status)
+		info->flags |=3D IEEE80211_TX_CTL_REQ_TX_STATUS;
+#endif
+
 	if (hdr->frame_control & cpu_to_le16(IEEE80211_STYPE_QOS_DATA)) {
 		tid =3D skb->priority & IEEE80211_QOS_CTL_TAG1D_MASK;
 		*ieee80211_get_qos_ctl(hdr) =3D tid;
=2D-
2.10.1 (Apple Git-78)