[PATCH v4 4/4] net: drop_monitor: use drop_reason_lookup()

[Johannes Berg <johannes@xxxxxxxxxxxxxxxx>]

From: Johannes Berg <johannes.berg@xxxxxxxxx>

Now that we have drop_reason_lookup(), we can just use it for
drop_monitor as well, rather than exporting the list itself.

Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
---
v3:
 - look up SKB_DROP_REASON_NOT_SPECIFIED if initial lookup
   returns NULL, to preserve previous behaviour
---
 include/net/dropreason.h |  4 ----
 net/core/drop_monitor.c  | 20 +++++---------------
 net/core/skbuff.c        |  6 +++---
 3 files changed, 8 insertions(+), 22 deletions(-)

diff --git a/include/net/dropreason.h b/include/net/dropreason.h
index c157070b5303..0e2195ccf2cd 100644
--- a/include/net/dropreason.h
+++ b/include/net/dropreason.h
@@ -38,10 +38,6 @@ struct drop_reason_list {
 	size_t n_reasons;
 };
 
-/* Note: due to dynamic registrations, access must be under RCU */
-extern const struct drop_reason_list __rcu *
-drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM];
-
 #ifdef CONFIG_TRACEPOINTS
 const char *drop_reason_lookup(unsigned long long value);
 void drop_reason_show(struct seq_file *m);
diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 430ed18f8584..fddf6b68bf06 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -610,9 +610,8 @@ static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
 				     size_t payload_len)
 {
 	struct net_dm_skb_cb *cb = NET_DM_SKB_CB(skb);
-	const struct drop_reason_list *list = NULL;
-	unsigned int subsys, subsys_reason;
 	char buf[NET_DM_MAX_SYMBOL_LEN];
+	const char *reason_str;
 	struct nlattr *attr;
 	void *hdr;
 	int rc;
@@ -630,19 +629,10 @@ static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
 		goto nla_put_failure;
 
 	rcu_read_lock();
-	subsys = u32_get_bits(cb->reason, SKB_DROP_REASON_SUBSYS_MASK);
-	if (subsys < SKB_DROP_REASON_SUBSYS_NUM)
-		list = rcu_dereference(drop_reasons_by_subsys[subsys]);
-	subsys_reason = cb->reason & ~SKB_DROP_REASON_SUBSYS_MASK;
-	if (!list ||
-	    subsys_reason >= list->n_reasons ||
-	    !list->reasons[subsys_reason] ||
-	    strlen(list->reasons[subsys_reason]) > NET_DM_MAX_REASON_LEN) {
-		list = rcu_dereference(drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_CORE]);
-		subsys_reason = SKB_DROP_REASON_NOT_SPECIFIED;
-	}
-	if (nla_put_string(msg, NET_DM_ATTR_REASON,
-			   list->reasons[subsys_reason])) {
+	reason_str = drop_reason_lookup(cb->reason);
+	if (unlikely(!reason_str))
+		reason_str = drop_reason_lookup(SKB_DROP_REASON_NOT_SPECIFIED);
+	if (nla_put_string(msg, NET_DM_ATTR_REASON, reason_str)) {
 		rcu_read_unlock();
 		goto nla_put_failure;
 	}
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index cd1ea6c3e0f8..bd4fb7410284 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -139,13 +139,11 @@ static const struct drop_reason_list drop_reasons_core = {
 	.n_reasons = ARRAY_SIZE(drop_reasons),
 };
 
-const struct drop_reason_list __rcu *
+static const struct drop_reason_list __rcu *
 drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM] = {
 	[SKB_DROP_REASON_SUBSYS_CORE] = RCU_INITIALIZER(&drop_reasons_core),
 };
-EXPORT_SYMBOL(drop_reasons_by_subsys);
 
-#ifdef CONFIG_TRACEPOINTS
 const char *drop_reason_lookup(unsigned long long value)
 {
 	unsigned long long subsys_id = value >> SKB_DROP_REASON_SUBSYS_SHIFT;
@@ -162,7 +160,9 @@ const char *drop_reason_lookup(unsigned long long value)
 		return NULL;
 	return subsys->reasons[reason];
 }
+EXPORT_SYMBOL(drop_reason_lookup);
 
+#ifdef CONFIG_TRACEPOINTS
 void drop_reason_show(struct seq_file *m)
 {
 	u32 subsys_id;
-- 
2.45.2