linux-kernel - Re: [PATCH v23 3/5] tracing: Allow user-space mapping of the ring-buffer

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Message-ID: <20240702173346.GA16408@altlinux.org>
Date: Tue, 2 Jul 2024 20:33:46 +0300
From: "Dmitry V. Levin" <ldv@...ace.io>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Vincent Donnefort <vdonnefort@...gle.com>, mhiramat@...nel.org,
	kernel-team@...roid.com, rdunlap@...radead.org, rppt@...nel.org,
	david@...hat.com, linux-trace-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v23 3/5] tracing: Allow user-space mapping of the
 ring-buffer

On Tue, Jul 02, 2024 at 11:18:07AM -0400, Steven Rostedt wrote:
> On Tue, 2 Jul 2024 10:36:03 -0400
> Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> 
> > > I can send a patch this week to update it. Or feel free to send a patch
> > > yourself.  
> > 
> > You need to reserve an unused ioctl Code and Seq# range within:
> > 
> > Documentation/userspace-api/ioctl/ioctl-number.rst
> 
> Ug, it's been so long, I completely forgot about that file.
> 
> Thanks for catching this.
> 
> > 
> > Otherwise this duplicate will confuse all system call instrumentation
> > tooling.
> 
> Agreed, what if we did this then:
> 
> -- Steve
> 
> diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
> index a141e8e65c5d..9a97030c6c8d 100644
> --- a/Documentation/userspace-api/ioctl/ioctl-number.rst
> +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
> @@ -186,6 +186,7 @@ Code  Seq#    Include File                                           Comments
>  'Q'   all    linux/soundcard.h
>  'R'   00-1F  linux/random.h                                          conflict!
>  'R'   01     linux/rfkill.h                                          conflict!
> +'R'   20-2F  linux/trace_mmap.h
>  'R'   C0-DF  net/bluetooth/rfcomm.h
>  'R'   E0     uapi/linux/fsl_mc.h
>  'S'   all    linux/cdrom.h                                           conflict!

Just in case, I've checked the list of ioctls known to strace and can
confirm that there are no users of 'R' ioctl code in 0x20..0x2f range yet.

By the way, this file is definitely not up to date, the 'R' part of it
should have contained the following:

'R'   00-1F  uapi/linux/random.h                                     conflict!
'R'   01-02  uapi/linux/rfkill.h                                     conflict!
'R'   01-0D  uapi/misc/fastrpc.h                                     conflict!
'R'   C0-DF  net/bluetooth/rfcomm.h
'R'   E0     uapi/linux/fsl_mc.h


-- 
ldv