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Subject: Re: [PATCH 0/3] support '%pd' and '%pD' for print file name
To: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
References: <20240119013848.3111364-1-yebin10@huawei.com>
 <20240119234356.1598e760edbfa58f5440a941@kernel.org>
CC: <rostedt@goodmis.org>, <mathieu.desnoyers@efficios.com>,
	<linux-trace-kernel@vger.kernel.org>, <linux-kernel@vger.kernel.org>
From: "yebin (H)" <yebin10@huawei.com>
Message-ID: <65AB679F.9070402@huawei.com>
Date: Sat, 20 Jan 2024 14:26:39 +0800
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On 2024/1/19 22:43, Masami Hiramatsu (Google) wrote:
> On Fri, 19 Jan 2024 09:38:45 +0800
> Ye Bin <yebin10@huawei.com> wrote:
>
>> During fault locating, the file name needs to be printed based on the
>> dentry/file address. The offset needs to be calculated each time, which
>> is troublesome. Similar to printk, kprobe supports printing file names
>> for dentry/file addresses.
> Hi Ye,
>
> 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)
>
> 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.
>
> Thank you,
Thank you very much for your suggestion.
I will re-implement this function according to your suggestion.
>> Ye Bin (3):
>>    tracing/probes: support '%pd' type for print struct dentry's name
>>    tracing/probes: support '%pD' type for print struct file's name
>>    Documentation: tracing: add new type 'pd' and 'pD' for kprobe
>>
>>   Documentation/trace/kprobetrace.rst |  3 +-
>>   kernel/trace/trace_probe.c          | 50 +++++++++++++++++++++++++++++
>>   2 files changed, 52 insertions(+), 1 deletion(-)
>>
>> -- 
>> 2.31.1
>>
>