[PATCH 1/2] nl80211: Retrieve maxattr via genl for nl80211

[Andrei Otcheretianski]

From: Benjamin Berg <benjamin.berg at intel.com>

Older kernel versions may not support all attributes and may refuse
commands that include them. To avoid sending too new attributes query
the highest supported attribute. This allows adding appropriate checks
where needed.

Signed-off-by: Benjamin Berg <benjamin.berg at intel.com>
---
 src/drivers/driver_nl80211.c | 28 ++++++++++++++++++++++++++++
 src/drivers/driver_nl80211.h |  1 +
 2 files changed, 29 insertions(+)

diff --git a/src/drivers/driver_nl80211.c b/src/drivers/driver_nl80211.c
index a3bb2d5251..b56ca852d3 100644
--- a/src/drivers/driver_nl80211.c
+++ b/src/drivers/driver_nl80211.c
@@ -16,6 +16,7 @@
 #include <net/if.h>
 #include <netlink/genl/genl.h>
 #include <netlink/genl/ctrl.h>
+#include <netlink/genl/family.h>
 #ifdef CONFIG_LIBNL3_ROUTE
 #include <netlink/route/neighbour.h>
 #endif /* CONFIG_LIBNL3_ROUTE */
@@ -1938,6 +1939,8 @@ static int wpa_driver_nl80211_get_country(void *priv, char *alpha2)
 
 static int wpa_driver_nl80211_init_nl_global(struct nl80211_global *global)
 {
+	struct nl_cache *cache = NULL;
+	struct genl_family *family = NULL;
 	int ret;
 
 	global->nl_cb = nl_cb_alloc(NL_CB_DEFAULT);
@@ -2009,6 +2012,29 @@ static int wpa_driver_nl80211_init_nl_global(struct nl80211_global *global)
 		/* Continue without vendor events */
 	}
 
+	/* Resolve maxattr for kernel support checks */
+	ret = genl_ctrl_alloc_cache(global->nl, &cache);
+	if (ret < 0) {
+		wpa_printf(MSG_DEBUG,
+			   "nl80211: Could not allocate genl cache: %d (%s)",
+			   ret, nl_geterror(ret));
+		goto err;
+	}
+
+	family = genl_ctrl_search(cache, global->nl80211_id);
+	if (!family) {
+		wpa_printf(MSG_DEBUG,
+			   "nl80211: Could not get nl80211 family from cache: %d (%s)",
+			   ret, nl_geterror(ret));
+		goto err;
+	}
+
+	global->nl80211_maxattr = genl_family_get_maxattr(family);
+	genl_family_put(family);
+	family = NULL;
+	nl_cache_free(cache);
+	cache = NULL;
+
 	nl_cb_set(global->nl_cb, NL_CB_SEQ_CHECK, NL_CB_CUSTOM,
 		  no_seq_check, NULL);
 	nl_cb_set(global->nl_cb, NL_CB_VALID, NL_CB_CUSTOM,
@@ -2021,6 +2047,8 @@ static int wpa_driver_nl80211_init_nl_global(struct nl80211_global *global)
 	return 0;
 
 err:
+	genl_family_put(family);
+	nl_cache_free(cache);
 	nl_destroy_handles(&global->nl_event);
 	nl_destroy_handles(&global->nl);
 	nl_cb_put(global->nl_cb);
diff --git a/src/drivers/driver_nl80211.h b/src/drivers/driver_nl80211.h
index 2b2bc9b117..315b88b01a 100644
--- a/src/drivers/driver_nl80211.h
+++ b/src/drivers/driver_nl80211.h
@@ -32,6 +32,7 @@ struct nl80211_global {
 	struct nl_cb *nl_cb;
 	struct nl_sock *nl;
 	int nl80211_id;
+	int nl80211_maxattr;
 	int nlctrl_id;
 	int ioctl_sock; /* socket for ioctl() use */
 
-- 
2.43.0