linux-kernel - RE: [PATCH v2] tracing/synthetic: use union instead of casts

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Date:   Mon, 14 Aug 2023 11:34:20 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Steven Rostedt' <rostedt@...dmis.org>,
        Sven Schnelle <svens@...ux.ibm.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] tracing/synthetic: use union instead of casts

From: Steven Rostedt
> Sent: 09 August 2023 13:55
> On Wed,  9 Aug 2023 09:14:59 +0200
> Sven Schnelle <svens@...ux.ibm.com> wrote:
> 
> > --- a/kernel/trace/trace.h
> > +++ b/kernel/trace/trace.h
> > @@ -1295,6 +1295,16 @@ static inline void trace_branch_disable(void)
> >  /* set ring buffers to default size if not already done so */
> >  int tracing_update_buffers(void);
> >
> > +struct trace_dynamic {
> > +	union {
> > +		u8				as_u8;
> > +		u16				as_u16;
> > +		u32				as_u32;
> > +		u64				as_u64;
> > +		struct trace_dynamic_info	as_dynamic;
> > +	};
> > +};
> > +
> 
> No need to create a structure around a single element union. Also, I would
> like to name it for what it is for.
> 
> union trace_synth_field {
> 	u8				as_u8;
> 	u16				as_u16;
> 	u32				as_u32;
> 	u64				as_u64;
> 	struct trace_dynamic_info	as_dynamic;
> };
> 
> Other than that, the patch looks good. Although I still need to test it.

I was wondering if you need the u8 and u16 members at all?
Can't the values just be treated as 32bit?
Both char and short aren't really 'proper' arithmetic types.

	David

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