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Date:   Wed, 16 Oct 2019 10:54:56 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Qu Wenruo <wqu@suse.com>
Cc:     linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-trace-devel@vger.kernel.org
Subject: Re: [PATCH] tools/lib/traceevent, perf tools: Handle %pU format
 correctly
Message-ID: <20191016105456.0b8d2310@gandalf.local.home>
In-Reply-To: <20191016063920.20791-1-wqu@suse.com>
References: <20191016063920.20791-1-wqu@suse.com>
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On Wed, 16 Oct 2019 14:39:20 +0800
Qu Wenruo <wqu@suse.com> wrote:

> +static void print_uuid_arg(struct trace_seq *s, void *data, int size,
> +			   struct tep_event *event, struct tep_print_arg *arg)
> +{
> +	const char *fmt;
> +	unsigned char *buf;
> +
> +	fmt = "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x";
> +	if (arg->type != TEP_PRINT_FIELD) {
> +		trace_seq_printf(s, "ARG TYPE NOT FIELID but %d", arg->type);
> +		return;
> +	}
> +
> +	if (!arg->field.field) {
> +		arg->field.field = tep_find_any_field(event, arg->field.name);
> +		if (!arg->field.field) {
> +			do_warning("%s: field %s not found",
> +				   __func__, arg->field.name);
> +			return;
> +		}
> +	}
> +	buf = data + arg->field.field->offset;

You also need to make sure the data field is not smaller than 16 bytes.

	if (arg->field.field->size < 16) {
		trace_seq_puts(s, "INVALIDUUID");
		return;
	}

> +
> +	trace_seq_printf(s, fmt, buf[0], buf[1], buf[2], buf[3], buf[4], buf[5],
> +		         buf[6], buf[7], buf[8], buf[9], buf[10], buf[11], buf[12],
> +			 buf[13], buf[14], buf[15]);
> +}
> +

Hmm, I know print_mac_addr() does something similar as this, but this
is getting a bit extreme (too many arguments!). What about doing:

	for (i = 0; i < 4; i++)
		trace_seq_printf(s, "%02x", buf++);

	for (i = 0; i < 3; i++)
		trace_seq_printf(s, "-%02x%02x", buf[i * 2], buf[i * 2 + 1]);

	buf += 6;

	trace_seq_putc(s, '-');

	for (i = 0; i < 6; i++)
		trace_seq_printf(s, "%02x", buf++);


Hmm, not sure the above is better, but having that many arguments just
looks ugly to me.

-- Steve