linux-kernel - Re: [PATCH 6/6] eventfs: clean up dentry ops and add revalidate function

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Message-Id: <20240201080715.80fadd15f38396c95bf39a00@kernel.org>
Date: Thu, 1 Feb 2024 08:07:15 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] eventfs: clean up dentry ops and add revalidate
 function

On Wed, 31 Jan 2024 13:00:39 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Tue, 30 Jan 2024 11:03:55 -0800
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > It would probably be cleaner to make eventfs its own filesystem, or at
> > least set its own dentry ops when looking up eventfs files.  But as it
> > is, only eventfs dentries use d_fsdata, so we don't really need to split
> > these things up by use.
> 
> BTW, I have been thinking about making eventfs a completely separate file
> system that could be mounted outside of tracefs. One that is readonly that
> only contains the "id" and "format" files and nothing more.
> 
> Why? Because perf and powertop both use those files to know how to parse
> the raw event formats. I don't think there's anything in there that
> requires root privileges to read. They should not be exposing any internal
> kernel information besides the event format layouts, and it would be nice
> to have a /sys/kernel/events directory that only had that.

That's a good idea! So maybe we can allow perf to read it without root user.

> 
> Making eventfs a separate file system where, when added to tracefs, has the
> control files for the specific trace_array, but for the /sys/kernel
> directory, only cares about the trace format files.
> 
> Then tracefs could be nicely converted over to kernfs, and eventfs would be
> its own entity.

If so, maybe we can just make symlinks to the 'id' and 'format' from events
under tracefs? :)

Thank you,

> 
> -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>