Re: [PATCH v2 6/6] Documentation: Describe console mouse reporting

[Randy Dunlap <rdunlap@infradead.org>]

On 7/1/20 8:14 AM, Tammo Block wrote:
> This patch adds a description of the kernel interface(s) used for vt
> console mouse reporting and describes the protocols and bitmasks.
> 
> Signed-off-by: Tammo Block <tammo.block@gmail.com>
> ---
>  .../admin-guide/console-mouse-reporting.rst   | 88 +++++++++++++++++++
>  Documentation/admin-guide/index.rst           |  1 +
>  2 files changed, 89 insertions(+)
>  create mode 100644 Documentation/admin-guide/console-mouse-reporting.rst
> 
> diff --git a/Documentation/admin-guide/console-mouse-reporting.rst b/Documentation/admin-guide/console-mouse-reporting.rst
> new file mode 100644
> index 000000000000..c75a627f27b8
> --- /dev/null
> +++ b/Documentation/admin-guide/console-mouse-reporting.rst
> @@ -0,0 +1,88 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=======================
> +Console Mouse Reporting
> +=======================
> +
> +A terminal may send escape sequences to enable applications to react to mouse
> +input. As the kernel does not know when to emit these events a mouse daemon
> +is needed to react to mouse movements and signal the kernel accordingly. The
> +kernel will then send an escape sequence to the application. This is called
> +mouse reporting and several types and protocols have been developed over time.
> +
> +See tiocl.h, the :manpage:`ioctl_console(2)` and :manpage:`console_codes(4)`
> +man pages and the xterm [1]_ or terminalguide [2]_ home pages for a detailed
> +list and description of the various protocols, their bit layout as well as
> +their limitations.
> +
> +Events and formats
> +++++++++++++++++++
> +
> +A Linux console keeps state about two different aspects of mouse reporting,
> +the kind of **events** to be reported and the **format** to send to userspace.
> +
> +A mouse daemon can check which kind of mouse events a client wants to be
> +informed about via the TIOCLINUX ioctl, using the TIOCL_GETMOUSEREPORTING
> +subcall. The values of the supported event classes (9, 1000, 1002, 1003) are
> +described in tiocl.h. Based on this information the daemon is responsible
> +for not sending data packages for unrequested events.
> +
> +A userspace client may request to be informed by the kernel about one of
> +the event classes and choose one of the data formats URXVT (1005), SRG
> +(1006) or X10/X11 (default) via console escape sequences. In general all
> +of them encode similar information, only the escape sequences differ.
> +
> +See the xterm [1]_ or terminalguide [2]_ home pages for all details.
> +
> +Reports from kernel to userspace client
> ++++++++++++++++++++++++++++++++++++++++
> +
> +The requested events are sent by the kernel to userspace encoded in an
> +escape sequences; details depend on the chosen format. All of them use one

          sequence;

(this word was correct in v1)

> +based pointer coordinates and a single byte to encode the button status.
> +
> +Short summary (we call this the SRG button format for the rest of this text):
> +
> + - 1,2 : Buttons, lower bits (see notes below)
> + - 3-5 : Modifier keys (Shift, Alt and Ctrl)
> + - 6   : Mouse movement only, no button status change
> + - 7-8 : Buttons, upper bits (for buttons 4-15)
> +
> +Reports sent from daemon to kernel
> +++++++++++++++++++++++++++++++++++
> +
> +A report is sent by a mouse daemon to the kernel via the TIOCLINUX ioctl,
> +using the TIOCL_SETSEL subcall. The coordinates are encoded zero based in
> +xs and ys, with 0,0 as the upper left corner, but see the note below.
> +The format used by the userspace mouse daemon for button encoding is almost
> +identical to the SRG button layout described above and is put into the sel_mode
> +of the tiocl_selection struct. All bits masked in TIOCL_SELBUTTONMASK are
> +unchanged compared to the SRG button format above; the remaining three are
> +changed the following way:
> +
> +- 3,4  : Unused, must be zero. The kernel knows modifier key state anyway.
> +- 5    : Always 1, identifies mouse report / TIOCL_SELMOUSEREPORT
> +
> +Notes
> ++++++
> +
> +Button numbers are encoded like this:
> +
> +- 0-2  : Left, middle and right button
> +- 3    : No button pressed / Button release
> +- 4-15 : More buttons, e.g. 4 and 5 are scroll wheel
> +
> +Please note that button releases should only be reported for buttons 0-2.
> +
> +Also note that coordinates (xs,ys,xe,ye) are zero based for the TIOCL_SETSEL
> +syscall but one based for the escape sequences sent by the kernel, so the
> +kernel will increase all coordinates by one.
> +
> +Older kernels only used the lower 4 bits of sel_mode, effectively limiting
> +the protocol to 3 buttons and button click only. The meaning of the 4 bits
> +is equivalent to the SRG button layout. Note that newer kernels will ignore
> +the upper two bits (modifier keys).
> +
> +.. [1] https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h2-Mouse-Tracking
> +.. [2] https://terminalguide.namepad.de/mouse/
> +

thanks.
-- 
~Randy