nl80211: allow splitting wiphy information in dumps

The per-wiphy information is getting large, to the point
where with more than the typical number of channels it's
too large and overflows, and userspace can't get any of
the information at all.

To address this (in a way that doesn't require making all
messages bigger) allow userspace to specify that it can
deal with wiphy information split across multiple parts
of the dump, and if it can split up the data. This also
splits up each channel separately so an arbitrary number
of channels can be supported.

Additionally, since GET_WIPHY has the same problem, add
support for filtering the wiphy dump and get information
for a single wiphy only, this allows userspace apps to
use dump in this case to retrieve all data from a single
device.

As userspace needs to know if all this this is supported,
add a global nl80211 feature set and include a bit for
this behaviour in it.

Cc: Dennis H Jensen <dennis.h.jensen@siemens.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/uapi/linux/nl80211.h

@@ -625,6 +625,10 @@
  *	%NL80211_ATTR_RADAR_EVENT is used to inform about the type of the
  *	event.
  *
+ * @NL80211_CMD_GET_PROTOCOL_FEATURES: Get global nl80211 protocol features,
+ *	i.e. features for the nl80211 protocol rather than device features.
+ *	Returns the features in the %NL80211_ATTR_PROTOCOL_FEATURES bitmap.
+ *
  * @NL80211_CMD_MAX: highest used command number
  * @__NL80211_CMD_AFTER_LAST: internal use
  */
@@ -779,6 +783,8 @@ enum nl80211_commands {
 
 	NL80211_CMD_RADAR_DETECT,
 
+	NL80211_CMD_GET_PROTOCOL_FEATURES,
+
 	/* add new commands above here */
 
 	/* used to define NL80211_CMD_MAX below */
@@ -1383,6 +1389,13 @@ enum nl80211_commands {
  *	advertised to the driver, e.g., to enable TDLS off channel operations
  *	and PU-APSD.
  *
+ * @NL80211_ATTR_PROTOCOL_FEATURES: global nl80211 feature flags, see
+ *	&enum nl80211_protocol_features, the attribute is a u32.
+ *
+ * @NL80211_ATTR_SPLIT_WIPHY_DUMP: flag attribute, userspace supports
+ *	receiving the data for a single wiphy split across multiple
+ *	messages, given with wiphy dump message
+ *
  * @NL80211_ATTR_MAX: highest attribute number currently defined
  * @__NL80211_ATTR_AFTER_LAST: internal use
  */
@@ -1669,6 +1682,9 @@ enum nl80211_attrs {
 	NL80211_ATTR_STA_CAPABILITY,
 	NL80211_ATTR_STA_EXT_CAPABILITY,
 
+	NL80211_ATTR_PROTOCOL_FEATURES,
+	NL80211_ATTR_SPLIT_WIPHY_DUMP,
+
 	/* add attributes here, update the policy in nl80211.c */
 
 	__NL80211_ATTR_AFTER_LAST,
@@ -3619,4 +3635,16 @@ enum nl80211_dfs_state {
 	NL80211_DFS_AVAILABLE,
 };
 
+/**
+ * enum enum nl80211_protocol_features - nl80211 protocol features
+ * @NL80211_PROTOCOL_FEATURE_SPLIT_WIPHY_DUMP: nl80211 supports splitting
+ *	wiphy dumps (if requested by the application with the attribute
+ *	%NL80211_ATTR_SPLIT_WIPHY_DUMP. Also supported is filtering the
+ *	wiphy dump by %NL80211_ATTR_WIPHY, %NL80211_ATTR_IFINDEX or
+ *	%NL80211_ATTR_WDEV.
+ */
+enum nl80211_protocol_features {
+	NL80211_PROTOCOL_FEATURE_SPLIT_WIPHY_DUMP =	1 << 0,
+};
+
 #endif /* __LINUX_NL80211_H */