Re: [PATCH v4 04/10] char-mux: add support for the terminal size

[Maximilian Immanuel Brandtner <maxbr@linux.ibm.com>]

On Fri, 2025-09-12 at 05:39 +0200, Filip Hejsek wrote:
> From: Szymon Lukasz <noh4hss@gmail.com>
> 
> The terminal size of a mux chardev should be the same as the real
> chardev, so listen for CHR_EVENT_RESIZE to be up to date.
> 
> We forward CHR_EVENT_RESIZE only to the focused frontend. This means
> frontends should probably update their view of the terminal size on
> receiving CHR_EVENT_MUX_IN.
> 
> Signed-off-by: Szymon Lukasz <noh4hss@gmail.com>
> Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
> ---
>  chardev/char-mux.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/chardev/char-mux.c b/chardev/char-mux.c
> index
> 6b36290e2c49f579580d2abb5aa552806f019d4a..4d3d05b82f13e002c766142f9d9
> c24977b8b9bd2 100644
> --- a/chardev/char-mux.c
> +++ b/chardev/char-mux.c
> @@ -264,9 +264,24 @@ void mux_chr_send_all_event(Chardev *chr,
> QEMUChrEvent event)
>      }
>  }
>  
> +static void mux_update_winsize(Chardev *chr)
> +{
> +    MuxChardev *d = MUX_CHARDEV(chr);
> +    uint16_t cols, rows;
> +
> +    qemu_chr_fe_get_winsize(&d->chr, &cols, &rows);
> +    qemu_chr_resize(chr, cols, rows);
> +}
> +
>  static void mux_chr_event(void *opaque, QEMUChrEvent event)
>  {
> -    mux_chr_send_all_event(CHARDEV(opaque), event);
> +    Chardev *chr = CHARDEV(opaque);
> +
> +    if (event == CHR_EVENT_RESIZE) {
> +        mux_update_winsize(chr);
> +    } else {
> +        mux_chr_send_all_event(chr, event);
> +    }
>  }
>  
>  static GSource *mux_chr_add_watch(Chardev *s, GIOCondition cond)
> @@ -382,6 +397,7 @@ static void qemu_chr_open_mux(Chardev *chr,
>       */
>      *be_opened = muxes_opened;
>      qemu_chr_fe_init(&d->chr, drv, errp);
> +    mux_update_winsize(chr);
>  }
>  
>  static void qemu_chr_parse_mux(QemuOpts *opts, ChardevBackend
> *backend,
> 

When changing the focussed chardev, the MuxChardev should send a resize
event to the newly focussed chardev. Otherwise the size information of
the focussed chardev might be outdated if it wasn't the focussed
chardev at the time of the resize event.

Theoretically, the resize event could also just be sent to all
character devices focussed or not, however as this causes a lot of
needless redrawing I prefer the approach of only resizing the focussed
chardev.

Kind regards,
Max Brandtner