[RFCv2 2/4] nl80211: Support >4096 byte NEW_WIPHY event nlmsg

[Denis Kenzior <denkenz@gmail.com>]

For historical reasons, NEW_WIPHY messages generated by dumps or
GET_WIPHY commands were limited to 4096 bytes due to userspace tools
using limited buffers.  Once the sizes NEW_WIPHY messages exceeded these
sizes, split dumps were introduced.  All any non-legacy data was added
only to messages using split-dumps (including filtered dumps).

However, split-dumping has quite a significant overhead.  On cards
tested, split dumps generated message sizes 1.7-1.8x compared to
non-split dumps, while still comfortably fitting into an 8k buffer.  The
kernel now expects userspace to provide 16k buffers by default, and 32k
buffers are possible.

Introduce a concept of a large message, so that if the kernel detects
that userspace has provided a buffer of sufficient size, a non-split
message could be generated.

Signed-off-by: Denis Kenzior <denkenz@gmail.com>
---
 net/wireless/nl80211.c | 51 ++++++++++++++++++++++++++++++------------
 1 file changed, 37 insertions(+), 14 deletions(-)

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index b9b0199b5ec6..682a095415eb 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -1839,6 +1839,7 @@ struct nl80211_dump_wiphy_state {
 	long start;
 	long split_start, band_start, chan_start, capa_start;
 	bool split;
+	bool large_message;
 };
 
 static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
@@ -2027,7 +2028,8 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 
 					if (nl80211_msg_put_channel(
 							msg, &rdev->wiphy, chan,
-							state->split))
+							state->split ||
+							state->large_message))
 						goto nla_put_failure;
 
 					nla_nest_end(msg, nl_freq);
@@ -2072,7 +2074,7 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 		i = nl80211_add_commands_unsplit(rdev, msg);
 		if (i < 0)
 			goto nla_put_failure;
-		if (state->split) {
+		if (state->split || state->large_message) {
 			CMD(crit_proto_start, CRIT_PROTOCOL_START);
 			CMD(crit_proto_stop, CRIT_PROTOCOL_STOP);
 			if (rdev->wiphy.flags & WIPHY_FLAG_HAS_CHANNEL_SWITCH)
@@ -2111,7 +2113,8 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 		/* fall through */
 	case 6:
 #ifdef CONFIG_PM
-		if (nl80211_send_wowlan(msg, rdev, state->split))
+		if (nl80211_send_wowlan(msg, rdev,
+					state->split || state->large_message))
 			goto nla_put_failure;
 		state->split_start++;
 		if (state->split)
@@ -2126,7 +2129,8 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 			goto nla_put_failure;
 
 		if (nl80211_put_iface_combinations(&rdev->wiphy, msg,
-						   state->split))
+						   state->split ||
+						   state->large_message))
 			goto nla_put_failure;
 
 		state->split_start++;
@@ -2145,7 +2149,7 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 		 * dump is split, otherwise it makes it too big. Therefore
 		 * only advertise it in that case.
 		 */
-		if (state->split)
+		if (state->split || state->large_message)
 			features |= NL80211_FEATURE_ADVERTISE_CHAN_LIMITS;
 		if (nla_put_u32(msg, NL80211_ATTR_FEATURE_FLAGS, features))
 			goto nla_put_failure;
@@ -2170,13 +2174,20 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 		 *
 		 * We still increment split_start so that in the split
 		 * case we'll continue with more data in the next round,
-		 * but break unconditionally so unsplit data stops here.
+		 * but break unless large_messages are requested, so
+		 * legacy unsplit data stops here.
 		 */
 		state->split_start++;
 
-		if (!state->split)
+		if (state->split)
+			break;
+
+		if (!state->large_message) {
 			state->split_start = 0;
-		break;
+			break;
+		}
+
+		/* Fall through */
 	case 9:
 		if (rdev->wiphy.extended_capabilities &&
 		    (nla_put(msg, NL80211_ATTR_EXT_CAPA,
@@ -2218,7 +2229,9 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 		}
 
 		state->split_start++;
-		break;
+		if (state->split)
+			break;
+		/* Fall through */
 	case 10:
 		if (nl80211_send_coalesce(msg, rdev))
 			goto nla_put_failure;
@@ -2234,7 +2247,9 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 			goto nla_put_failure;
 
 		state->split_start++;
-		break;
+		if (state->split)
+			break;
+		/* Fall through */
 	case 11:
 		if (rdev->wiphy.n_vendor_commands) {
 			const struct nl80211_vendor_cmd_info *info;
@@ -2270,7 +2285,9 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 			nla_nest_end(msg, nested);
 		}
 		state->split_start++;
-		break;
+		if (state->split)
+			break;
+		/* Fall through */
 	case 12:
 		if (rdev->wiphy.flags & WIPHY_FLAG_HAS_CHANNEL_SWITCH &&
 		    nla_put_u8(msg, NL80211_ATTR_MAX_CSA_COUNTERS,
@@ -2312,7 +2329,9 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 		}
 
 		state->split_start++;
-		break;
+		if (state->split)
+			break;
+		/* Fall through */
 	case 13:
 		if (rdev->wiphy.num_iftype_ext_capab &&
 		    rdev->wiphy.iftype_ext_capab) {
@@ -2380,13 +2399,17 @@ static int nl80211_send_wiphy(struct cfg80211_registered_device *rdev,
 		}
 
 		state->split_start++;
-		break;
+		if (state->split)
+			break;
+		/* Fall through */
 	case 14:
 		if (nl80211_send_pmsr_capa(rdev, msg))
 			goto nla_put_failure;
 
 		state->split_start++;
-		break;
+		if (state->split)
+			break;
+		/* Fall through */
 	case 15:
 		if (rdev->wiphy.akm_suites &&
 		    nla_put(msg, NL80211_ATTR_AKM_SUITES,
-- 
2.21.0