Re: [PATCH v3 1/5] vt: Add cursor-size helpers

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Sep 28, 2026 at 10:55:24AM +0200, Thomas Zimmermann wrote:
> Cursors in the VT subsystem are blocks within a character cell that are
> filled with the foreground color. The new helpers vc_cursor_start() and
> vc_cursor_end() return the scanlines in which the cursor block starts rsp.
> ends. This is compatible with VGA hardware.
> 
> In terms of cursor design, the new cursor-size helpers follow established
> styles in fbcon. The only exception is in underline cursors for fonts with
> a size larger than 10. The underlining dash is now one pixel closer to
> the font-glyph data, so that the cursor looks less detached. This follows
> the style used by vgacon.
> 
> Users control the cursor size with the vt module's parameter cur_default
> or with the ESC sequence \e[?Nc, where N is the cursor-size constant. In
> case of an invalid setting, the new helpers fall back to cur_default and
> then underline cursors; in this order.
> 
> Similar code in vgacon and fbcon ignores the cursor's default size stored
> in vt.cur_default. The consoles default to full-block cursors, while vt
> defaults to underline cursors. VGA BIOSes also tend to use underline by.
> default. Upon initialization vt applies its default to the console, but
> each console might fall back to it own default. For example, running the
> ESC code from above with the invalid constant of 8 magically flips the
> cursor from underline to block size on vgacon. Another call with N set
> to 0 (i.e., default) magically flips it back to underlyine. Making
> underline the new default everywhere harmonizes vt, fbcon and most VGA
> BIOSes.
> 
> v3:
> - mention user interfaces to control cursor size in commit message (GregKH)
> - elaborate defaults (GregKH)
> - move retry logic into helper
> - handle CUR_DEF
> v2:
> - export non-font interface for vgacon
> - avoid interference from concurrent user space (Sashiko)
> - fix function docs (Sashiko)
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Reviewed-by: Helge Deller <deller@gmx.de>
> ---
>  drivers/tty/vt/vt.c            | 104 +++++++++++++++++++++++++++++++++
>  include/linux/console_struct.h |   7 +++
>  2 files changed, 111 insertions(+)

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>