nl80211: add generation number to all dumps

In order for userspace to be able to figure out whether
it obtained a consistent snapshot of data or not when
using netlink dumps, we need to have a generation number
in each dump message that indicates whether the list has
changed or not -- its value is arbitrary.

This patch adds such a number to all dumps, this needs
some mac80211 involvement to keep track of a generation
number to start with when adding/removing mesh paths or
stations.

The wiphy and netdev lists can be fully handled within
cfg80211, of course, but generation numbers need to be
stored there as well.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

2 files changed, 24 insertions, 5 deletions

diff --git a/include/linux/nl80211.h b/include/linux/nl80211.h
index cb3dc6027fd..a8d71ed43a0 100644
--- a/include/linux/nl80211.h
+++ b/include/linux/nl80211.h
@@ -480,10 +480,6 @@ enum nl80211_commands {
  * @NL80211_ATTR_SCAN_FREQUENCIES: nested attribute with frequencies (in MHz)
  * @NL80211_ATTR_SCAN_SSIDS: nested attribute with SSIDs, leave out for passive
  *	scanning and include a zero-length SSID (wildcard) for wildcard scan
- * @NL80211_ATTR_SCAN_GENERATION: the scan generation increases whenever the
- *	scan result list changes (BSS expired or added) so that applications
- *	can verify that they got a single, consistent snapshot (when all dump
- *	messages carried the same generation number)
  * @NL80211_ATTR_BSS: scan result BSS
  *
  * @NL80211_ATTR_REG_INITIATOR: indicates who requested the regulatory domain
@@ -580,6 +576,14 @@ enum nl80211_commands {
  *
  * @NL80211_ATTR_PID: Process ID of a network namespace.
  *
+ * @NL80211_ATTR_GENERATION: Used to indicate consistent snapshots for
+ *	dumps. This number increases whenever the object list being
+ *	dumped changes, and as such userspace can verify that it has
+ *	obtained a complete and consistent snapshot by verifying that
+ *	all dump messages contain the same generation number. If it
+ *	changed then the list changed and the dump should be repeated
+ *	completely from scratch.
+ *
  * @NL80211_ATTR_MAX: highest attribute number currently defined
  * @__NL80211_ATTR_AFTER_LAST: internal use
  */
@@ -651,7 +655,7 @@ enum nl80211_attrs {
 
 	NL80211_ATTR_SCAN_FREQUENCIES,
 	NL80211_ATTR_SCAN_SSIDS,
-	NL80211_ATTR_SCAN_GENERATION,
+	NL80211_ATTR_GENERATION, /* replaces old SCAN_GENERATION */
 	NL80211_ATTR_BSS,
 
 	NL80211_ATTR_REG_INITIATOR,
@@ -716,6 +720,9 @@ enum nl80211_attrs {
 	NL80211_ATTR_MAX = __NL80211_ATTR_AFTER_LAST - 1
 };
 
+/* source-level API compatibility */
+#define NL80211_ATTR_SCAN_GENERATION NL80211_ATTR_GENERATION
+
 /*
  * Allow user space programs to use #ifdef on new attributes by defining them
  * here
diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index 1ee30fcd6fd..de7d116acc3 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -372,6 +372,10 @@ struct rate_info {
  * @txrate: current unicast bitrate to this station
  * @rx_packets: packets received from this station
  * @tx_packets: packets transmitted to this station
+ * @generation: generation number for nl80211 dumps.
+ *	This number should increase every time the list of stations
+ *	changes, i.e. when a station is added or removed, so that
+ *	userspace can tell whether it got a consistent snapshot.
  */
 struct station_info {
 	u32 filled;
@@ -385,6 +389,8 @@ struct station_info {
 	struct rate_info txrate;
 	u32 rx_packets;
 	u32 tx_packets;
+
+	int generation;
 };
 
 /**
@@ -444,6 +450,10 @@ enum mpath_info_flags {
  * @flags: mesh path flags
  * @discovery_timeout: total mesh path discovery timeout, in msecs
  * @discovery_retries: mesh path discovery retries
+ * @generation: generation number for nl80211 dumps.
+ *	This number should increase every time the list of mesh paths
+ *	changes, i.e. when a station is added or removed, so that
+ *	userspace can tell whether it got a consistent snapshot.
  */
 struct mpath_info {
 	u32 filled;
@@ -454,6 +464,8 @@ struct mpath_info {
 	u32 discovery_timeout;
 	u8 discovery_retries;
 	u8 flags;
+
+	int generation;
 };
 
 /**