[PATCH] tracing/ipv4/ipv6: Give size to name field in fib*_lookup_table event

[PATCH] tracing/ipv4/ipv6: Give size to name field in fib*_lookup_table event

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.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.

Considering that the intent was to only reserve the size needed for the
name and not a fixed size, convert the size part of the __dynamic_array()
field to contain the necessary code to determine the size needed to save
the name.

Alternatively, if the intent was to use a fixed size, then it should be
converted into __array() of type char, which will remove the meta data in
the event that stores the size.

Cc: David Ahern <dsahern@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/trace/events/fib.h  | 2 +-
 include/trace/events/fib6.h | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/trace/events/fib.h b/include/trace/events/fib.h
index 6f2a4dc35e37..76f925f5519a 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 )
+		__dynamic_array(char,  name,   nhc && nhc->nhc_dev ? strlen(nhc->nhc_dev->name) + 1 : sizeof("-") )
 	),
 
 	TP_fast_assign(
diff --git a/include/trace/events/fib6.h b/include/trace/events/fib6.h
index c6abdcc77c12..d3aee58e58fd 100644
--- a/include/trace/events/fib6.h
+++ b/include/trace/events/fib6.h
@@ -31,7 +31,8 @@ TRACE_EVENT(fib6_table_lookup,
 		__field(        u16,	dport		)
 		__field(        u8,	proto		)
 		__field(        u8,	rt_type		)
-		__dynamic_array(	char,	name,	IFNAMSIZ )
+		__dynamic_array(	char,	name,	res->nh && res->nh->fib_nh_dev ?
+							strlen(res->nh->fib_nh_dev->name) + 1 : sizeof("-") )
 		__array(		__u8,	gw,	16	 )
 	),
 
-- 
2.35.1

Re: [PATCH] tracing/ipv4/ipv6: Give size to name field in fib*_lookup_table event

[David Ahern]

On 7/3/22 8:23 AM, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.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.
> 
> Considering that the intent was to only reserve the size needed for the
> name and not a fixed size, convert the size part of the __dynamic_array()
> field to contain the necessary code to determine the size needed to save
> the name.
> 
> Alternatively, if the intent was to use a fixed size, then it should be
> converted into __array() of type char, which will remove the meta data in
> the event that stores the size.

I would prefer this option over duplicating the all of the checks to
save 14B.

Re: [PATCH] tracing/ipv4/ipv6: Give size to name field in fib*_lookup_table event

[Steven Rostedt]

On Sun, 3 Jul 2022 13:03:20 -0600
David Ahern <dsahern@gmail.com> wrote:


> > Alternatively, if the intent was to use a fixed size, then it should be
> > converted into __array() of type char, which will remove the meta data in
> > the event that stores the size.  
> 
> I would prefer this option over duplicating the all of the checks to
> save 14B.

That's why I mentioned the alternative. To give you that option.

I'll send a v2 later that uses the static array.

-- Steve