linux-kernel - Re: [PATCH v2 2/3] perf: convert: fix duplicate field names and avoid reserved keywords.

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Message-ID: <20150130152537.GA10543@home.goodmis.org>
Date:	Fri, 30 Jan 2015 10:25:37 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	jolsa@...hat.com, jeremie.galarneau@...icios.com,
	alexmonthy@...populi.im, bigeasy@...utronix.de, lizefan@...wei.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] perf: convert: fix duplicate field names and
 avoid reserved keywords.

On Mon, Jan 26, 2015 at 06:38:24PM +0800, Wang Nan wrote:
> (If Steven Rostedt accept the previous patch which introduce a priv
>  field to 'struct format_field', we can use a relative simple method
>  for name conversion. If not , perf must track name conversion by
>  itself.)

Sorry for coming in so late here.

> 
> Some parameters of syscall tracepoints named as 'nr', 'event', etc.
> When dealing with them, perf convert to ctf meets some problem:
> 
>  1. If a parameter with name 'nr', it will duplicate syscall's
>     common field 'nr'. One such syscall is io_submit().
> 
>  2. If a parameter with name 'event', it is denied to be inserted
>     because 'event' is a babeltrace keywork. One such syscall is
>     epoll_ctl.
> 
> This patch appends '_dupl_X' suffix to avoid problem 1, prepend a '_'
> prefix to avoid problem 2.

Actually, I don't like this approach. That is, to have this private
data structure. Why not just add an "alias" to format_field. In other
words, instead of hiding this interaction behind a void pointer and 
needing to create a function pointer to free it, just add another
field to format field and be done with it. I think it would make
the code a hell of a lot simpler and easier to understand.

 struct format_field {
 	struct format_field	*next;
	struct event_format	*event;
	char			*type;
	char			*name;
+	char			*alias;
	int			offset;
	int			size;
	unsigned int		arraylen;
	unsigned int		elementsize;
	unsigned long		flags;
};

And put the logic in event parse to free alias if need be.
Heck, you could even add a pevent_*() func to assign the alias
using strdup, or what not.

-- Steve

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