linux-kernel - Re: [PATCH v7 1/5] tracing/probes: support '%pd' type for print struct dentry's name

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Message-ID: <20240321114636.5ed19630@gandalf.local.home>
Date: Thu, 21 Mar 2024 11:46:36 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Ye Bin <yebin10@...wei.com>, <mathieu.desnoyers@...icios.com>,
 <linux-trace-kernel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 1/5] tracing/probes: support '%pd' type for print
 struct dentry's name

On Fri, 22 Mar 2024 00:07:59 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> > What would be really useful is if we had a way to expose BTF here. Something like:
> > 
> >  "%pB:<struct>:<field>"
> > 
> > The "%pB" would mean to look up the struct/field offsets and types via BTF,
> > and create the appropriate command to find and print it.  
> 
> Would you mean casing the pointer to "<struct>"?

I mean, instead of having:

 ":%pd"

We could have:

 "+0(*:%pB:dentry:name):string"

Where the parsing could use BTF to see that this is a pointer to "struct dentry"
and the member field is "name".

This would also allow pretty much any other structure dereference.
That is if BTF gives structure member offsets?

-- Steve