linux-kernel - [for-linus][PATCH] tracing: Have memmapped ring buffer use ioctl of "R" range 0x20-2F

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Message-ID: <20240703164247.34096efa@rorschach.local.home>
Date: Wed, 3 Jul 2024 16:42:46 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, "Dmitry V. Levin" <ldv@...ace.io>,
 Jonathan Corbet <corbet@....net>
Subject: [for-linus][PATCH] tracing: Have memmapped ring buffer use ioctl of
 "R" range 0x20-2F


It was reported that the ioctl() number used to update the ring buffer
memory mapping conflicted with the TCGETS ioctl causing strace to report:

  $ strace -e ioctl stty
  ioctl(0, TCGETS or TRACE_MMAP_IOCTL_GET_READER, {c_iflag=ICRNL|IXON, c_oflag=NL0|CR0|TAB0|BS0|VT0|FF0|OPOST|ONLCR, c_cflag=B38400|CS8|CREAD, c_lflag=ISIG|ICANON|ECHO|ECHOE|ECHOK|IEXTEN|ECHOCTL|ECHOKE, ...}) = 0

Since this ioctl hasn't been in a full release yet, change it from "T", 0x1
to "R" 0x20, and also reserve 0x20-0x2F for future ioctl commands, as
some more are being worked on for the future.

  git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
trace/urgent

Head SHA1: 4ecaf7e98a3ae0c843d67c76649ecc694232834b


Steven Rostedt (Google) (1):
      tracing: Have memmapped ring buffer use ioctl of "R" range 0x20-2F

----
 Documentation/userspace-api/ioctl/ioctl-number.rst | 1 +
 include/uapi/linux/trace_mmap.h                    | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)
---------------------------
commit 4ecaf7e98a3ae0c843d67c76649ecc694232834b
Author: Steven Rostedt (Google) <rostedt@...dmis.org>
Date:   Tue Jul 2 15:33:54 2024 -0400

    tracing: Have memmapped ring buffer use ioctl of "R" range 0x20-2F
    
    To prevent conflicts with other ioctl numbers to allow strace to have an
    idea of what is happening, add the range of ioctls for the trace buffer
    mapping from _IO("T", 0x1) to the range of "R" 0x20 - 0x2F.
    
    Link: https://lore.kernel.org/linux-trace-kernel/20240630105322.GA17573@altlinux.org/
    Link: https://lore.kernel.org/linux-trace-kernel/20240630213626.GA23566@altlinux.org/
    
    Cc: Jonathan Corbet <corbet@....net>
    Fixes: cf9f0f7c4c5bb ("tracing: Allow user-space mapping of the ring-buffer")
    Link: https://lore.kernel.org/20240702153354.367861db@rorschach.local.home
    Reported-by: "Dmitry V. Levin" <ldv@...ace.io>
    Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
    Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
    Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>

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_ */