On Fri, 19 Jan 2024 10:52:43 -0500
Steven Rostedt [off-list ref] wrote:

On Fri, 19 Jan 2024 23:43:56 +0900
Masami Hiramatsu (Google) [off-list ref] wrote:

quoted

Thanks for your proposal!

Generically, I think this type of hack is not good for the tracing
because there are already some ways to do that. e.g.
 - Use perf probe to specify dentry->name:string or file->name:string 
 - Use BTF to specify in the same way (but only for function entry)
And those are more obvious what it does.

However, if this is implemented in more generic syntax, it will be
acceptable.
For example, type specifying with "arg1:printfmt(%pD)" will be
more generic because it is apparently one of the printfmt and output
string. Or, maybe we can just allow to use ":%pD" as a fetch type
(start with '%' means the printfmt)

Yes, I like this idea a lot. Please add the '%' keyword/token to change how
to display this in the print format.

We may need to add more than one token though. Is that supported?

  $arg1:u32:%08x

or that could also be:

  $arg1:%08x:u32

No, not yet. But I rather like comma separated.

$arg1:u32,%08x

Hm, this needs more changes, like a new type parser. And it will be
a option of the default type.

Thank you, 

That is, the order should not be important.

Thoughts?

-- Steve

quoted

Also, could you update readme_msg[] in kernel/trace/trace.c if
you add a type, and add a testcase of selftests/ftrace, for this
feature? Documentation should also be updated with more syntax
information.

-- 
Masami Hiramatsu (Google) [off-list ref]