[PATCH 0/1] nl80211: add NL80211_CMD_GET_TSF

[PATCH 0/1] nl80211: add NL80211_CMD_GET_TSF

[Rohan Joyce]

Hi,

This is a followup to the original discussion about having a way to query the
TSF value for a wireless interface from userspace[1]. Rather than using the
sysfs method proposed there, it adds a new command to nl80211. I've tried to
conform to the way in which existing nl80211 commands are written.

[1] http://comments.gmane.org/gmane.linux.kernel.wireless.general/117485

Rohan Joyce (1):
  nl80211: add NL80211_CMD_GET_TSF

 include/net/cfg80211.h       |  6 ++++++
 include/uapi/linux/nl80211.h | 10 ++++++++++
 net/mac80211/cfg.c           | 16 +++++++++++++++
 net/wireless/nl80211.c       | 47 ++++++++++++++++++++++++++++++++++++++++++++
 net/wireless/rdev-ops.h      | 11 +++++++++++
 net/wireless/trace.h         | 18 +++++++++++++++++
 6 files changed, 108 insertions(+)

-- 
2.1.0

[PATCH 1/1] nl80211: add NL80211_CMD_GET_TSF

[Rohan Joyce]

This patch adds a command NL80211_CMD_GET_TSF that retrieves the 64 bit time
synchronisation value for an interface. It returns the value in a uint64
attribute of type NL80211_ATTR_TSF.

Signed-off-by: Rohan Joyce <rojoyce.github@gmail.com>
---
 include/net/cfg80211.h       |  6 ++++++
 include/uapi/linux/nl80211.h | 10 ++++++++++
 net/mac80211/cfg.c           | 16 +++++++++++++++
 net/wireless/nl80211.c       | 47 ++++++++++++++++++++++++++++++++++++++++++++
 net/wireless/rdev-ops.h      | 11 +++++++++++
 net/wireless/trace.h         | 18 +++++++++++++++++
 6 files changed, 108 insertions(+)

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index 64e09e1..9425d11 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -2415,6 +2415,9 @@ struct cfg80211_qos_map {
  *	and returning to the base channel for communication with the AP.
  * @tdls_cancel_channel_switch: Stop channel-switching with a TDLS peer. Both
  *	peers must be on the base channel when the call completes.
+ *
+ * @get_tsf: Get the current value of the time synchronization function for the
+ *	given interface
  */
 struct cfg80211_ops {
 	int	(*suspend)(struct wiphy *wiphy, struct cfg80211_wowlan *wow);
@@ -2678,6 +2681,9 @@ struct cfg80211_ops {
 	void	(*tdls_cancel_channel_switch)(struct wiphy *wiphy,
 					      struct net_device *dev,
 					      const u8 *addr);
+
+	int     (*get_tsf)(struct wiphy *wiphy, struct net_device *dev,
+			   u64 *tsf);
 };
 
 /*
diff --git a/include/uapi/linux/nl80211.h b/include/uapi/linux/nl80211.h
index 68b294e..a8d228e 100644
--- a/include/uapi/linux/nl80211.h
+++ b/include/uapi/linux/nl80211.h
@@ -798,6 +798,10 @@
  *	as an event to indicate changes for devices with wiphy-specific regdom
  *	management.
  *
+ * @NL80211_CMD_GET_TSF: Get timing synchronisation function value for the
+ *	interface identified by %NL80211_ATTR_IFINDEX. The command returns
+ *	the value in a %NL80211_ATTR_TSF.
+ *
  * @NL80211_CMD_MAX: highest used command number
  * @__NL80211_CMD_AFTER_LAST: internal use
  */
@@ -984,6 +988,8 @@ enum nl80211_commands {
 
 	NL80211_CMD_WIPHY_REG_CHANGE,
 
+	NL80211_CMD_GET_TSF,
+
 	/* add new commands above here */
 
 	/* used to define NL80211_CMD_MAX below */
@@ -1740,6 +1746,8 @@ enum nl80211_commands {
  * @NL80211_ATTR_SCHED_SCAN_DELAY: delay before a scheduled scan (or a
  *	WoWLAN net-detect scan) is started, u32 in seconds.
  *
+ * @NL80211_ATTR_TSF: time synchronization function value, u64.
+ *
  * @NUM_NL80211_ATTR: total number of nl80211_attrs available
  * @NL80211_ATTR_MAX: highest attribute number currently defined
  * @__NL80211_ATTR_AFTER_LAST: internal use
@@ -2107,6 +2115,8 @@ enum nl80211_attrs {
 
 	NL80211_ATTR_SCHED_SCAN_DELAY,
 
+	NL80211_ATTR_TSF,
+
 	/* add attributes here, update the policy in nl80211.c */
 
 	__NL80211_ATTR_AFTER_LAST,
diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index dd4ff36..77a823f 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -3734,6 +3734,21 @@ static int ieee80211_del_tx_ts(struct wiphy *wiphy, struct net_device *dev,
 	return -ENOENT;
 }
 
+static int ieee80211_get_tsf(struct wiphy *wiphy, struct net_device *dev,
+			     u64 *tsf)
+{
+	struct ieee80211_local *local = wiphy_priv(wiphy);
+	struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
+
+	if (!local->ops->get_tsf)
+		return -EOPNOTSUPP;
+
+	*tsf = drv_get_tsf(local, sdata);
+
+	return 0;
+}
+
+
 const struct cfg80211_ops mac80211_config_ops = {
 	.add_virtual_intf = ieee80211_add_iface,
 	.del_virtual_intf = ieee80211_del_iface,
@@ -3818,4 +3833,5 @@ const struct cfg80211_ops mac80211_config_ops = {
 	.set_ap_chanwidth = ieee80211_set_ap_chanwidth,
 	.add_tx_ts = ieee80211_add_tx_ts,
 	.del_tx_ts = ieee80211_del_tx_ts,
+	.get_tsf = ieee80211_get_tsf,
 };
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index e9ad9d9..cadd954 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -399,6 +399,7 @@ static const struct nla_policy nl80211_policy[NUM_NL80211_ATTR] = {
 	[NL80211_ATTR_WIPHY_SELF_MANAGED_REG] = { .type = NLA_FLAG },
 	[NL80211_ATTR_NETNS_FD] = { .type = NLA_U32 },
 	[NL80211_ATTR_SCHED_SCAN_DELAY] = { .type = NLA_U32 },
+	[NL80211_ATTR_TSF] = { .type = NLA_U64 },
 };
 
 /* policy for the key attributes */
@@ -1534,6 +1535,7 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 			if (rdev->wiphy.features &
 					NL80211_FEATURE_SUPPORTS_WMM_ADMISSION)
 				CMD(add_tx_ts, ADD_TX_TS);
+			CMD(get_tsf, GET_TSF);
 		}
 		/* add into the if now */
 #undef CMD
@@ -10145,6 +10147,43 @@ static int nl80211_tdls_cancel_channel_switch(struct sk_buff *skb,
 	return 0;
 }
 
+static int nl80211_get_tsf(struct sk_buff *skb, struct genl_info *info)
+{
+	struct cfg80211_registered_device *rdev = info->user_ptr[0];
+	struct net_device *dev = info->user_ptr[1];
+	struct sk_buff *msg;
+	void *hdr;
+	u64 tsf;
+	int err;
+
+	if (!rdev->ops->get_tsf)
+		return -EOPNOTSUPP;
+
+	err = rdev_get_tsf(rdev, dev, &tsf);
+	if (err)
+		return err;
+
+	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
+
+	hdr = nl80211hdr_put(msg, info->snd_portid, info->snd_seq, 0,
+			     NL80211_CMD_GET_TSF);
+	if (!hdr)
+		goto nla_put_failure;
+
+	if (nla_put_u64(msg, NL80211_ATTR_TSF, tsf))
+		goto nla_put_failure;
+
+	genlmsg_end(msg, hdr);
+	return genlmsg_reply(msg, info);
+
+ nla_put_failure:
+	err = -ENOBUFS;
+	nlmsg_free(msg);
+	return err;
+}
+
 #define NL80211_FLAG_NEED_WIPHY		0x01
 #define NL80211_FLAG_NEED_NETDEV	0x02
 #define NL80211_FLAG_NEED_RTNL		0x04
@@ -10960,6 +10999,14 @@ static const struct genl_ops nl80211_ops[] = {
 		.internal_flags = NL80211_FLAG_NEED_NETDEV_UP |
 				  NL80211_FLAG_NEED_RTNL,
 	},
+	{
+		.cmd = NL80211_CMD_GET_TSF,
+		.doit = nl80211_get_tsf,
+		.policy = nl80211_policy,
+		.flags = GENL_ADMIN_PERM,
+		.internal_flags = NL80211_FLAG_NEED_NETDEV_UP |
+				  NL80211_FLAG_NEED_RTNL,
+	}
 };
 
 /* notification functions */
diff --git a/net/wireless/rdev-ops.h b/net/wireless/rdev-ops.h
index 35cfb71..9729da9 100644
--- a/net/wireless/rdev-ops.h
+++ b/net/wireless/rdev-ops.h
@@ -1017,4 +1017,15 @@ rdev_tdls_cancel_channel_switch(struct cfg80211_registered_device *rdev,
 	trace_rdev_return_void(&rdev->wiphy);
 }
 
+static inline int rdev_get_tsf(struct cfg80211_registered_device *rdev,
+			       struct net_device *dev, u64 *tsf)
+{
+	int ret = -EOPNOTSUPP;
+	if (rdev->ops->get_tsf) {
+		ret = rdev->ops->get_tsf(&rdev->wiphy, dev, tsf);
+		trace_rdev_get_tsf(&rdev->wiphy, dev, *tsf);
+	}
+	return ret;
+}
+
 #endif /* __CFG80211_RDEV_OPS */
diff --git a/net/wireless/trace.h b/net/wireless/trace.h
index b17b369..4dc800d 100644
--- a/net/wireless/trace.h
+++ b/net/wireless/trace.h
@@ -2077,6 +2077,24 @@ TRACE_EVENT(rdev_tdls_cancel_channel_switch,
 		  WIPHY_PR_ARG, NETDEV_PR_ARG, MAC_PR_ARG(addr))
 );
 
+TRACE_EVENT(rdev_get_tsf,
+	TP_PROTO(struct wiphy *wiphy, struct net_device *netdev,
+		 u64 tsf),
+	TP_ARGS(wiphy, netdev, tsf),
+	TP_STRUCT__entry(
+		WIPHY_ENTRY
+		NETDEV_ENTRY
+		__field(u64, tsf)
+	),
+	TP_fast_assign(
+		WIPHY_ASSIGN;
+		NETDEV_ASSIGN;
+		__entry->tsf = tsf;
+	),
+	TP_printk(WIPHY_PR_FMT ", " NETDEV_PR_FMT ", tsf: %llu",
+		  WIPHY_PR_ARG, NETDEV_PR_ARG, __entry->tsf)
+);
+
 /*************************************************************
  *	     cfg80211 exported functions traces		     *
  *************************************************************/
-- 
2.1.0

Re: [PATCH 1/1] nl80211: add NL80211_CMD_GET_TSF

[Johannes Berg]

On Mon, 2015-02-23 at 21:57 +0800, Rohan Joyce wrote:
> This patch adds a command NL80211_CMD_GET_TSF that retrieves the 64 bit time
> synchronisation value for an interface. It returns the value in a uint64
> attribute of type NL80211_ATTR_TSF.

This should explain why and how this could possibly be used - I don't
see any reasonable usage since the TSF is quickly changing and this API
doesn't really allow for any synchronisation.

johannes

Re: [PATCH 1/1] nl80211: add NL80211_CMD_GET_TSF

[Rohan Joyce]

Hi,

The motivation for this patch is to assist using a WiiU Gamepad with Linux. 
The WiiU Gamepad is an input device that also contains an LCD touchscreen,
speakers and a variety of sensors. The Gamepad connects to an access
point (usually the WiiU console itself, but it can be coerced to connect
to a properly configured hostap). The Gamepad provides five services over
UDP. Two of the services that are provided (audio and video streaming to
the device) use the TSF as a timestamp in the application layer. The
firmware on the Gamepad checks to make sure that incoming packets for
these services have timestamps within 1000us of its own internal clock,
which is synced to the TSF of the access point.

At the moment, users who want to use this device have to manually apply 
a kernel patch similar to that which was first posted to this list a year
ago. This patch is my attempt to implement the functionality using a more
conventional API and make it easier for end users.

Should I include protocol implementation details specific to this device in
the documentation of the NL80211_CMD_GET_TSF command?

Thanks for your time,

Rohan

Re: [PATCH 1/1] nl80211: add NL80211_CMD_GET_TSF

[Johannes Berg]

On Mon, 2015-02-23 at 23:38 +0800, Rohan Joyce wrote:
> Hi,
> 
> The motivation for this patch is to assist using a WiiU Gamepad with Linux. 
> The WiiU Gamepad is an input device that also contains an LCD touchscreen,
> speakers and a variety of sensors. The Gamepad connects to an access
> point (usually the WiiU console itself, but it can be coerced to connect
> to a properly configured hostap). The Gamepad provides five services over
> UDP. Two of the services that are provided (audio and video streaming to
> the device) use the TSF as a timestamp in the application layer. The
> firmware on the Gamepad checks to make sure that incoming packets for
> these services have timestamps within 1000us of its own internal clock,
> which is synced to the TSF of the access point.

Oh, right, I remember now.

> At the moment, users who want to use this device have to manually apply 
> a kernel patch similar to that which was first posted to this list a year
> ago. This patch is my attempt to implement the functionality using a more
> conventional API and make it easier for end users.
> 
> Should I include protocol implementation details specific to this device in
> the documentation of the NL80211_CMD_GET_TSF command?

Not necessarily, but some information about why this is needed would be
good.

I guess since this has no way of using something like 11v this really is
the only chance.

Note that you'll need to add a feature capability flag for this - many
drivers, even ones based on mac80211, will not be able to implement this
properly so relying only on the presence of the callback will not work
properly.

johannes