Re: [PATCH RFC 2/2] perf: convert: fix duplicate field names and avoid reserved keywords.

From: Wang Nan <wangnan0@huawei.com>
To: Jiri Olsa <jolsa@redhat.com>, <jeremie.galarneau@efficios.com>
Cc: <rostedt@goodmis.org>, <bigeasy@linutronix.de>,
	<lizefan@huawei.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC 2/2] perf: convert: fix duplicate field names and avoid reserved keywords.
Date: Fri, 23 Jan 2015 09:57:53 +0800	[thread overview]
Message-ID: <54C1AAA1.4000300@huawei.com> (raw)
In-Reply-To: <20150122132734.GB2473@krava.brq.redhat.com>

On 2015/1/22 21:27, Jiri Olsa wrote:
> On Thu, Jan 22, 2015 at 01:36:43PM +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.)
>>
>> 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.
> 
> I've got compilation error:
> 
> util/data-convert-bt.c: In function ‘event_class_add_field’:
> util/data-convert-bt.c:629:2: error: suggest parentheses around assignment used as truth value [-Werror=parentheses]
>   while (t = bt_ctf_event_class_get_field_by_name(event_class, name)) {
> 
> what's your gcc version? mine's caught that..
> 

I also curious why you got so many Werror problems I'm not ever seen,
until I found a '-w' in my gcc options, which is introduced by your commit

47810c1d429bc690e1f5e9467697538921962171: perf data: Disable Werror convert object.

I'll revert that commit in my tree.

> [jolsa@krava perf]$ gcc --version
> gcc (GCC) 4.8.3 20140911 (Red Hat 4.8.3-7)
> 
> SNIP
> 
>>  
>> +/* If dup < 0, add a prefix. Else, add _dupl_X suffix. */
>> +static char *change_name(char *name, char *orig_name, int dup)
>> +{
>> +	char *new_name = NULL;
>> +	size_t len;
>> +
>> +	if (!name)
>> +		name = orig_name;
>> +
>> +	if (dup >= 10)
>> +		goto out;
>> +
>> +	if (dup < 0)
>> +		len = strlen(name) + sizeof("_");
>> +	else
>> +		len = strlen(orig_name) + sizeof("_dupl_X");
> 
> if we allow for _dupl_10, should we use 'sizeof("_dupl_x")' ^^^ in here?
> 
>> +
>> +	new_name = malloc(len);
>> +	if (!new_name)
>> +		goto out;
>> +
>> +	if (dup < 0)
>> +		snprintf(new_name, len, "_%s", name);
>> +	else
>> +		snprintf(new_name, len, "%s_dupl_%d", orig_name, dup);
>> +
>> +out:
>> +	if (name != orig_name)
>> +		free(name);
>> +	return new_name;
> 
> SNIP
> 
>> +
>> +	name = field->name;
>> +	while (t = bt_ctf_event_class_get_field_by_name(event_class, name)) {
>> +		bt_ctf_field_type_put(t);
>> +		name = change_name(name, field->name, dup++);
>> +		if (!name) {
>> +			pr_err("Failed to create dup name for '%s'\n", field->name);
>> +			return -1;
>> +		}
>> +	}
>> +
>> +	ret = bt_ctf_event_class_add_field(event_class, type, name);
>> +
>> +	/* if failed, we may hit a keywork. try again with a '_' prefix */
>> +	if (ret) {
>> +		name = change_name(name, field->name, -1);
>> +		if (!name) {
>> +			pr_err("Failed to alloc name for '_%s'\n", field->name);
>> +			return -1;
>> +		}
>> +		ret = bt_ctf_event_class_add_field(event_class, type, name);
> 
> so there's no other way on checking up with the blacklist right?
> 

AFAIK there's no official method to check blacklist right now. Utilizing existing
functions to check blacklist is possible. For example, we can create a clock using
bt_ctf_clock_create() with the checked name and then free it. However, it is hacky
and I think you won't like it.

I believe my solution should be acceptable before babeltrace export its
validate_identifier() function to users. Jérémie Galarneau, do you have better
idea on it?

Thanks.

> thanks,
> jirka
> 