Received-SPF: pass (google.com: domain of linux-kernel+bounces-31327-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Date: Fri, 19 Jan 2024 10:52:43 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Ye Bin <yebin10@huawei.com>, <mathieu.desnoyers@efficios.com>,
 <linux-trace-kernel@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/3] support '%pd' and '%pD' for print file name
Message-ID: <20240119105243.05082e5b@gandalf.local.home>
In-Reply-To: <20240119234356.1598e760edbfa58f5440a941@kernel.org>
References: <20240119013848.3111364-1-yebin10@huawei.com>
	<20240119234356.1598e760edbfa58f5440a941@kernel.org>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit

On Fri, 19 Jan 2024 23:43:56 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> 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

That is, the order should not be important.

Thoughts?

-- Steve


> 
> 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.