linux-kernel - Re: [PATCH] vt: add support for smput/rmput escape codes

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Message-ID: <e5f75c37-30a5-4c4e-aae5-a72060be24da@kernel.org>
Date: Mon, 25 Aug 2025 07:47:10 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Calixte Pernot <calixte.pernot@...noble-inp.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH] vt: add support for smput/rmput escape codes

Hi,

On 24. 08. 25, 16:20, Calixte Pernot wrote:
> Support "\e[?1049h" and "\e[?1049l" escape codes.
> This patch allows programs to enter and leave alternate screens.
> This feature is widely available in graphical terminal emulators and mostly
> used by fullscreen terminal-based user interfaces such as text editors.
> Most editors such as vim and nano assume this escape code in not supported
> and will not try to print the escape sequence if TERM=linux.
> To try out this patch, run `TERM=xterm-256color vim` inside a VT.
> 
> Signed-off-by: Calixte Pernot <calixte.pernot@...noble-inp.org>
...
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
...
> @@ -1878,6 +1883,46 @@ static int get_bracketed_paste(struct tty_struct *tty)
>   	return vc->vc_bracketed_paste;
>   }
>   
> +/* console_lock is held */
> +static void enter_alt_screen(struct vc_data *vc)
> +{
> +	unsigned int size = vc->vc_rows * vc->vc_cols * 2;
> +
> +	if (vc->vc_saved_screen != NULL)
> +		return; /* Already inside an alt-screen */

All this is protected by console_lock, right?

> +	vc->vc_saved_screen = kzalloc(size, GFP_NOWAIT);

Why GFP_NOWAIT?

> +	if (vc->vc_saved_screen == NULL)
> +		return;
> +	memcpy(vc->vc_saved_screen, (u16 *)vc->vc_origin, size);

kmemdup();

> +	vc->vc_saved_rows = vc->vc_rows;
> +	vc->vc_saved_cols = vc->vc_cols;
> +	save_cur(vc);
> +	/* clear entire screen */
> +	csi_J(vc, CSI_J_FULL);
> +}
> +
> +/* console_lock is held */
> +static void leave_alt_screen(struct vc_data *vc)
> +{
> +	unsigned int rows = min(vc->vc_saved_rows, vc->vc_rows);
> +	unsigned int cols = min(vc->vc_saved_cols, vc->vc_cols);
> +	unsigned short *src, *dest;

u16

> +
> +	if (vc->vc_saved_screen == NULL)
> +		return; /* Not inside an alt-screen */
> +	for (int r = 0; r < rows; r++) {

unsigned

> +		src = vc->vc_saved_screen + r * vc->vc_saved_cols;
> +		dest = ((u16 *)vc->vc_origin) + r * vc->vc_cols;
> +		memcpy(dest, src, 2 * cols);
> +	}
> +	restore_cur(vc);
> +	/* Update the entire screen */
> +	if (con_should_update(vc))
> +		do_update_region(vc, vc->vc_origin, vc->vc_screenbuf_size / 2);
> +	kfree(vc->vc_saved_screen);
> +	vc->vc_saved_screen = NULL;
> +}
...
> --- a/include/linux/console_struct.h
> +++ b/include/linux/console_struct.h
> @@ -159,6 +159,9 @@ struct vc_data {
>   	struct uni_pagedict *uni_pagedict;
>   	struct uni_pagedict **uni_pagedict_loc; /* [!] Location of uni_pagedict variable for this console */
>   	u32 **vc_uni_lines;			/* unicode screen content */
> +	unsigned short	*vc_saved_screen;

u16 *

> +	unsigned int	vc_saved_cols;
> +	unsigned int	vc_saved_rows;
>   	/* additional information is in vt_kern.h */
>   };
>   

thanks,
-- 
js
suse labs