linux-kernel - [PATCH v2] tracing/ipv4/ipv6: Use static array for name field in fib*_lookup

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Message-ID: <20220704091436.3705edbf@rorschach.local.home>
Date:   Mon, 4 Jul 2022 09:14:36 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     David Ahern <dsahern@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>
Subject: [PATCH v2] tracing/ipv4/ipv6: Use static array for name field in
 fib*_lookup_table event

From: "Steven Rostedt (Google)" <rostedt@...dmis.org>

The fib_lookup_table and fib6_lookup_table events declare name as a
dynamic_array, but also give it a fixed size, which defeats the purpose of
the dynamic array, especially since the dynamic array also includes meta
data in the event to specify its size.

Since the size of the name is at most 16 bytes (defined by IFNAMSIZ),
it is not worth spending the effort to determine the size of the string.

Just use a fixed size array and copy into it. This will save 4 bytes that
are used for the meta data that saves the size and position of a dynamic
array, and even slightly speed up the event processing.

Cc: David Ahern <dsahern@...il.com>
Cc: David S. Miller <davem@...emloft.net>
Cc: netdev@...r.kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
Changes since v1: https://lkml.kernel.org/r/20220703102359.30f12e39@rorschach.local.home
 - Just use a fixed size array instead of calculating the
   size needed for the dynamic allocation.

 include/trace/events/fib.h  | 6 +++---
 include/trace/events/fib6.h | 8 ++++----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/trace/events/fib.h b/include/trace/events/fib.h
index 6f2a4dc35e37..c2300c407f58 100644
--- a/include/trace/events/fib.h
+++ b/include/trace/events/fib.h
@@ -32,7 +32,7 @@ TRACE_EVENT(fib_table_lookup,
 		__array(	__u8,	gw6,	16	)
 		__field(	u16,	sport		)
 		__field(	u16,	dport		)
-		__dynamic_array(char,  name,   IFNAMSIZ )
+		__array(char,  name,   IFNAMSIZ )
 	),
 
 	TP_fast_assign(
@@ -66,7 +66,7 @@ TRACE_EVENT(fib_table_lookup,
 		}
 
 		dev = nhc ? nhc->nhc_dev : NULL;
-		__assign_str(name, dev ? dev->name : "-");
+		strlcpy(__entry->name, dev ? dev->name : "-", IFNAMSIZ);
 
 		if (nhc) {
 			if (nhc->nhc_gw_family == AF_INET) {
@@ -95,7 +95,7 @@ TRACE_EVENT(fib_table_lookup,
 		  __entry->tb_id, __entry->oif, __entry->iif, __entry->proto,
 		  __entry->src, __entry->sport, __entry->dst, __entry->dport,
 		  __entry->tos, __entry->scope, __entry->flags,
-		  __get_str(name), __entry->gw4, __entry->gw6, __entry->err)
+		  __entry->name, __entry->gw4, __entry->gw6, __entry->err)
 );
 #endif /* _TRACE_FIB_H */
 
diff --git a/include/trace/events/fib6.h b/include/trace/events/fib6.h
index c6abdcc77c12..6e821eb79450 100644
--- a/include/trace/events/fib6.h
+++ b/include/trace/events/fib6.h
@@ -31,7 +31,7 @@ TRACE_EVENT(fib6_table_lookup,
 		__field(        u16,	dport		)
 		__field(        u8,	proto		)
 		__field(        u8,	rt_type		)
-		__dynamic_array(	char,	name,	IFNAMSIZ )
+		__array(		char,	name,	IFNAMSIZ )
 		__array(		__u8,	gw,	16	 )
 	),
 
@@ -63,9 +63,9 @@ TRACE_EVENT(fib6_table_lookup,
 		}
 
 		if (res->nh && res->nh->fib_nh_dev) {
-			__assign_str(name, res->nh->fib_nh_dev);
+			strlcpy(__entry->name, res->nh->fib_nh_dev->name, IFNAMSIZ);
 		} else {
-			__assign_str(name, "-");
+			strcpy(__entry->name, "-");
 		}
 		if (res->f6i == net->ipv6.fib6_null_entry) {
 			struct in6_addr in6_zero = {};
@@ -83,7 +83,7 @@ TRACE_EVENT(fib6_table_lookup,
 		  __entry->tb_id, __entry->oif, __entry->iif, __entry->proto,
 		  __entry->src, __entry->sport, __entry->dst, __entry->dport,
 		  __entry->tos, __entry->scope, __entry->flags,
-		  __get_str(name), __entry->gw, __entry->err)
+		  __entry->name, __entry->gw, __entry->err)
 );
 
 #endif /* _TRACE_FIB6_H */
-- 
2.35.1