linux-kernel - Re: [PATCH] f2fs: Fix f2fs_truncate_partial

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Message-ID: <ZNo8hoR2V3Zo14+l@e126311.manchester.arm.com>
Date:   Mon, 14 Aug 2023 15:39:02 +0100
From:   Kajetan Puchalski <kajetan.puchalski@....com>
To:     Douglas RAILLARD <douglas.raillard@....com>
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "open list:F2FS FILE SYSTEM" <linux-f2fs-devel@...ts.sourceforge.net>,
        "open list:TRACING" <linux-kernel@...r.kernel.org>,
        "open list:TRACING" <linux-trace-kernel@...r.kernel.org>,
        jstultz@...gle.com, qyousef@...gle.com, lukasz.luba@....com
Subject: Re: [PATCH] f2fs: Fix f2fs_truncate_partial_nodes ftrace event

On Mon, Aug 14, 2023 at 02:32:53PM +0100, Kajetan Puchalski wrote:
> On Mon, Mar 06, 2023 at 12:25:49PM +0000, Douglas RAILLARD wrote:
> > From: Douglas Raillard <douglas.raillard@....com>
> > 
> > Fix the nid_t field so that its size is correctly reported in the text
> > format embedded in trace.dat files. As it stands, it is reported as
> > being of size 4:
> > 
> >         field:nid_t nid[3];     offset:24;      size:4; signed:0;
> > 
> > Instead of 12:
> > 
> >         field:nid_t nid[3];     offset:24;      size:12;        signed:0;
> > 
> > This also fixes the reported offset of subsequent fields so that they
> > match with the actual struct layout.
> > 
> > 
> > Signed-off-by: Douglas Raillard <douglas.raillard@....com>
> > ---
> >  include/trace/events/f2fs.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
> > index 31d994e6b4ca..8d053838d6cf 100644
> > --- a/include/trace/events/f2fs.h
> > +++ b/include/trace/events/f2fs.h
> > @@ -512,7 +512,7 @@ TRACE_EVENT(f2fs_truncate_partial_nodes,
> >  	TP_STRUCT__entry(
> >  		__field(dev_t,	dev)
> >  		__field(ino_t,	ino)
> > -		__field(nid_t,	nid[3])
> > +		__array(nid_t,	nid, 3)
> >  		__field(int,	depth)
> >  		__field(int,	err)
> >  	),
> > -- 
> > 2.25.1
> 
> Hi,
> 
> Just wanted to flag that I noticed this breaks Perfetto tracing on
> Android, at least as of Android 13. I'm not sure if it's been fixed in newer
> versions. Looks like the version of Perfetto in Android 13 is expecting
> the previous (ie broken) field format to be there and its entire ftrace
> collector fails as a result:
> 
> E/perfetto( 3532): ranslation_table.cc:133 Failed to infer ftrace field type for "f2fs_truncate_partial_nodes.nid" (type:"nid_t nid[3]" size:12 signed:0) (errno: 2, No such file or directory)
> I/perfetto( 3640):            probes.cc:65 Hard resetting ftrace state.
> 
> For my own purposes I just reverted these two:
> * 0b04d4c0542e8573a837b1d81b94209e48723b25 (f2fs: Fix f2fs_truncate_partial_nodes ftrace event)
> * f82e7ca019dfad3b006fd3b772f7ac569672db55 (tracing: Error if a trace event has an array for a __field()
> 
> and now it works fine so not the biggest deal but this should probably
> be addressed, I imagine more likely on the Perfetto side.

Added context here, it is just caused by the parser implementation in Perfetto
being pretty lacking:

https://github.com/google/perfetto/blob/c36c70c1d4a72eafdd257f7a63e55f49fbc3df3d/src/traced/probes/ftrace/proto_translation_table.cc#L255