linux-kernel - Re: [PATCH v2 2/2] tracing: Use seq_buf_hex

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Message-ID: <20191126145101.1e6c4e43@gandalf.local.home>
Date:   Tue, 26 Nov 2019 14:51:01 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Piotr Maziarz <piotrx.maziarz@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        andriy.shevchenko@...el.com, cezary.rojewski@...el.com,
        gustaw.lewandowski@...el.com
Subject: Re: [PATCH v2 2/2] tracing: Use seq_buf_hex_dump() to dump buffers

On Tue, 26 Nov 2019 15:53:26 +0100
Piotr Maziarz <piotrx.maziarz@...ux.intel.com> wrote:
> Hello Steven,
> 
> I'm writing handle in event-parse and I came across some technical 
> problems. I have an event which print function looks like that:
> TP_printk("%s",
> 	  __print_hex_dump("", DUMP_PREFIX_OFFSET, 16, 4,
> 			   __get_dynamic_array(buf),
> 			   __get_dynamic_array_len(buf), false))
> It works properly when printing events to debugfs.
> I'm testing my implementation with trace-cmd and it has problem with 
> parsing DUMP_PREFIX_OFFSET and false (I'm using 
> alloc_and_process_delim()). Instead of having numerical values 
> tep_print_args are of type TEP_PRINT_ATOM and have char array 
> "DUMP_PREFIX_OFFSET" or "true".
> Am I doing something incorrect? Parsing it this way is problematic 
> because instead of false someone may use 0 or logic expression. And 
> writing it to support all possible scenarios may be tedious and prone to 
> errors.

You can force the enum to be a number by including the following in the
trace event header:

TRACE_DEFINE_ENUM(DUMP_PREFIX_OFFSET);
TRACE_DEFINE_ENUM(DUMP_PREFIX_ADDRESS);
TRACE_DEFINE_ENUM(DUMP_PREFIX_NONE);

and the format files will convert these to their actual numbers when
displaying it to user space.

-- Steve