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From: Johannes Berg <johannes@sipsolutions.net>
To: linux-kernel@vger.kernel.org
Cc: linux-trace-kernel@vger.kernel.org,
	netdev@vger.kernel.org,
	linux-wireless@vger.kernel.org,
	Johannes Berg <johannes.berg@intel.com>
Subject: [RFC PATCH v2 2/4] net: dropreason: use new __print_sym() in tracing
Date: Tue, 26 Mar 2024 20:15:57 +0100
Message-ID: <20240326202131.fcbc8a528439.I075de1ac698b47710b94c631afdfb328f07be961@changeid>
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From: Johannes Berg <johannes.berg@intel.com>

The __print_symbolic() could only ever print the core
drop reasons, since that's the way the infrastructure
works. Now that we have __print_sym() with all the
advantages mentioned in that commit, convert to that
and get all the drop reasons from all subsystems. As
we already have a list of them, that's really easy.

This is a little bit of .text (~100 bytes in my build)
and saves a lot of .data (~17k).

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 include/net/dropreason.h   |  5 +++++
 include/trace/events/skb.h | 16 +++-----------
 net/core/skbuff.c          | 43 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+), 13 deletions(-)

diff --git a/include/net/dropreason.h b/include/net/dropreason.h
index 56cb7be92244..c157070b5303 100644
--- a/include/net/dropreason.h
+++ b/include/net/dropreason.h
@@ -42,6 +42,11 @@ struct drop_reason_list {
 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);
+#endif
+
 void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
 				  const struct drop_reason_list *list);
 void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys);
diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
index 07e0715628ec..8a1a63f9e796 100644
--- a/include/trace/events/skb.h
+++ b/include/trace/events/skb.h
@@ -8,15 +8,9 @@
 #include <linux/skbuff.h>
 #include <linux/netdevice.h>
 #include <linux/tracepoint.h>
+#include <net/dropreason.h>
 
-#undef FN
-#define FN(reason)	TRACE_DEFINE_ENUM(SKB_DROP_REASON_##reason);
-DEFINE_DROP_REASON(FN, FN)
-
-#undef FN
-#undef FNe
-#define FN(reason)	{ SKB_DROP_REASON_##reason, #reason },
-#define FNe(reason)	{ SKB_DROP_REASON_##reason, #reason }
+TRACE_DEFINE_SYM_FNS(drop_reason, drop_reason_lookup, drop_reason_show);
 
 /*
  * Tracepoint for free an sk_buff:
@@ -44,13 +38,9 @@ TRACE_EVENT(kfree_skb,
 
 	TP_printk("skbaddr=%p protocol=%u location=%pS reason: %s",
 		  __entry->skbaddr, __entry->protocol, __entry->location,
-		  __print_symbolic(__entry->reason,
-				   DEFINE_DROP_REASON(FN, FNe)))
+		  __print_sym(__entry->reason, drop_reason ))
 );
 
-#undef FN
-#undef FNe
-
 TRACE_EVENT(consume_skb,
 
 	TP_PROTO(struct sk_buff *skb, void *location),
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index b99127712e67..012b48da8810 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -147,6 +147,49 @@ drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM] = {
 };
 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;
+	u32 reason = value & ~SKB_DROP_REASON_SUBSYS_MASK;
+	const struct drop_reason_list *subsys;
+
+	if (subsys_id >= SKB_DROP_REASON_SUBSYS_NUM)
+		return NULL;
+
+	subsys = rcu_dereference(drop_reasons_by_subsys[subsys_id]);
+	if (!subsys)
+		return NULL;
+	if (reason >= subsys->n_reasons)
+		return NULL;
+	return subsys->reasons[reason];
+}
+
+void drop_reason_show(struct seq_file *m)
+{
+	u32 subsys_id;
+
+	rcu_read_lock();
+	for (subsys_id = 0; subsys_id < SKB_DROP_REASON_SUBSYS_NUM; subsys_id++) {
+		const struct drop_reason_list *subsys;
+		u32 i;
+
+		subsys = rcu_dereference(drop_reasons_by_subsys[subsys_id]);
+		if (!subsys)
+			continue;
+
+		for (i = 0; i < subsys->n_reasons; i++) {
+			if (!subsys->reasons[i])
+				continue;
+			seq_printf(m, ", { %u, \"%s\" }",
+				   (subsys_id << SKB_DROP_REASON_SUBSYS_SHIFT) | i,
+				   subsys->reasons[i]);
+		}
+	}
+	rcu_read_unlock();
+}
+#endif
+
 /**
  * drop_reasons_register_subsys - register another drop reason subsystem
  * @subsys: the subsystem to register, must not be the core
-- 
2.44.0