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

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Date: Tue, 2 Jul 2024 11:18:07 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: "Dmitry V. Levin" <ldv@...ace.io>, 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, 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!
diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h
index bd1066754220..c102ef35d11e 100644
--- a/include/uapi/linux/trace_mmap.h
+++ b/include/uapi/linux/trace_mmap.h
@@ -43,6 +43,6 @@ struct trace_buffer_meta {
 	__u64	Reserved2;
 };

-#define TRACE_MMAP_IOCTL_GET_READER		_IO('T', 0x1)
+#define TRACE_MMAP_IOCTL_GET_READER		_IO('R', 0x20)

 #endif /* _TRACE_MMAP_H_ */