Re: [PATCH 4/5] ftrace: show ftrace_bprintk()'s formats

[Lai Jiangshan <laijs@cn.fujitsu.com>]

Jason Baron wrote:
> On Wed, Dec 31, 2008 at 10:56:23AM +0800, Lai Jiangshan wrote:
>> Impact: let user knows the format
>>
>> Create a file on <debugfs-dir>/tracing/ to show ftrace_bprintk()'s formats.
>>
>> This formats will help for these condition:
>> 1) User get binary data from core file.(formats are backup before coredump)
>> 2) User splice ring_buffer to a file.
>> User can use formats for parsing the binary data in userspace.
>>
> 
> When I 'cat' trace_bprintk_formats on my system the file is empty. This
> seems to be b/c 'ftrace_bprintk' is not being used in this patchset. It
> can't be used in patch #5 during marker register b/c the format wouldn't
> be known at runtime. Thus, as it currently stands this patch, patch 4/5,
> isn't adding much?

If you don't use ftrace_bprintk(), the file trace_bprintk_formats is empty.
This file record all formats which ftrace_bprintk() uses.

You can use ftrace_bprintk() everywhere as another printk().

Patch #5 enables binary printk for markers, this is another additional tool
for tracing markers.

> 
> A thought on how this might be resolved would be to have the core marker
> code pass us its address so this could be recorded in the trace buffer.
> Then, also add some debug file that displays the markers and maps marker
> addresses with format strings.
> 

Patch#5 does it as you said.