linux-kernel - Re: [PATCH v2 1/2] tracing/events: make _

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Message-ID: <20090527072956.GC24381@infradead.org>
Date:	Wed, 27 May 2009 03:30:02 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Christoph Hellwig <hch@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Jens Axboe <jens.axboe@...cle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Theodore Ts'o <tytso@....edu>,
	Steven Whitehouse <swhiteho@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] tracing/events: make __string() more general

On Wed, May 27, 2009 at 09:43:32AM +0800, Li Zefan wrote:
> I'm not suffering from NULL str, so I'm not quite sure how you want __string()
> deal with it.

The internals of __string is still magic to me, need to finish my
advance cpp abuse degree first ;-)

But the expected outcome would be that when we get a NULL pointer as
input we get a NULL pointer as output again.

What I currently do is:

TRACE_EVENT(xfs_dir2,
	TP_PROTO(struct xfs_da_args *args, int i, int j, int count),
	TP_ARGS(args, i, j, count),

	TP_STRUCT__entry(
		__field(xfs_ino_t, ino)
		__array(char, name, TRACE_MAXNAMELEN)
		__field(int, namelen)
		...
	),

        TP_fast_assign(
		__entry->ino = args->dp->i_ino;
		if (args->namelen)
			memcpy(__entry->name, args->name,
			       min(args->namelen, TRACE_MAXNAMELEN));
		__entry->namelen = args->namelen;
		...
	),

	TP_printk("ino 0x%lld %pF name %.*s namelen %d hashval 0x%x "
		  "inumber 0x%llx op_flags %s i %d j %d count %d",
		  __entry->ino,
		  (void *)__entry->caller_ip,
		  min(__entry->namelen, TRACE_MAXNAMELEN),
		  __entry->namelen ? __entry->name : NULL,
		  __entry->namelen,
		  ...)
);

> 
> 
---end quoted text---
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