linux-kernel - Re: [PATCH 1/2 v4] scsi: add __print

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Date:	Fri, 02 Apr 2010 10:40:53 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	rostedt@...dmis.org
CC:	Kei Tokunaga <tokunaga.keiich@...fujitsu.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	James Bottomley <James.Bottomley@...e.de>,
	Ingo Molnar <mingo@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Tomohiro Kusumi <kusumi.tomohiro@...fujitsu.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Subject: Re: [PATCH 1/2 v4] scsi: add __print_hex() to ftrace

>> +const char *
>> +ftrace_print_hex_seq(struct trace_seq *p, const unsigned char *buf, int buf_len)
>> +{
>> +	int i;
>> +	const char *ret = p->buffer + p->len;
>> +
>> +	for (i = 0; i < buf_len; i++)
>> +		trace_seq_printf(p, "%s%2.2x", i == 0 ? "" : " ", buf[i]);
>> +
>> +	trace_seq_putc(p, 0);
> 
> I would not put the putc(p, 0) into a helper function. This terminates
> the buffer, and strings added to the trace_seq will go after the '\0'.
> 

This is exactly what ftrace_print_flags_seq() and ftrace_print_symbols_seq()
do, and exactly what we want.

An example:

TP_printk("%s,%s", __print_flags(...), __print_flags(...));

We need 2 seperated strings, while trace_seq_terminate() will make it
a single string.

> What we need is this in trace_seq.h:
> 
> static inline trace_seq_terminate(struct trace_seq *s)
> {
> 	if (!s->full)
> 		s->buffer[s->len] = 0;
> }
> 
> This will add a '0' to the buffer after the last string, but will not
> increment length while doing it. Thus, new data added to the buffer
> would still be appended correctly.
> 
> -- Steve
> 
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL(ftrace_print_hex_seq);
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