[PATCH] vt: add support for smput/rmput escape codes

[PATCH] vt: add support for smput/rmput escape codes

[Calixte Pernot]

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@grenoble-inp.org>
---
 drivers/tty/vt/vt.c            | 59 ++++++++++++++++++++++++++++++++++
 include/linux/console_struct.h |  3 ++
 2 files changed, 62 insertions(+)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 62049ceb3..0e3632aa1 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -141,6 +141,7 @@ static const struct consw *con_driver_map[MAX_NR_CONSOLES];
 static int con_open(struct tty_struct *, struct file *);
 static void vc_init(struct vc_data *vc, int do_clear);
 static void gotoxy(struct vc_data *vc, int new_x, int new_y);
+static void restore_cur(struct vc_data *vc);
 static void save_cur(struct vc_data *vc);
 static void reset_terminal(struct vc_data *vc, int do_clear);
 static void con_flush_chars(struct tty_struct *tty);
@@ -1344,6 +1345,10 @@ struct vc_data *vc_deallocate(unsigned int currcons)
 		kfree(vc->vc_screenbuf);
 		vc_cons[currcons].d = NULL;
 	}
+	if (vc->vc_saved_screen != NULL) {
+		kfree(vc->vc_saved_screen);
+		vc->vc_saved_screen = NULL;
+	}
 	return vc;
 }
 
@@ -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 */
+	vc->vc_saved_screen = kzalloc(size, GFP_NOWAIT);
+	if (vc->vc_saved_screen == NULL)
+		return;
+	memcpy(vc->vc_saved_screen, (u16 *)vc->vc_origin, size);
+	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;
+
+	if (vc->vc_saved_screen == NULL)
+		return; /* Not inside an alt-screen */
+	for (int r = 0; r < rows; r++) {
+		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;
+}
+
 enum {
 	CSI_DEC_hl_CURSOR_KEYS	= 1,	/* CKM: cursor keys send ^[Ox/^[[x */
 	CSI_DEC_hl_132_COLUMNS	= 3,	/* COLM: 80/132 mode switch */
@@ -1888,6 +1933,7 @@ enum {
 	CSI_DEC_hl_MOUSE_X10	= 9,
 	CSI_DEC_hl_SHOW_CURSOR	= 25,	/* TCEM */
 	CSI_DEC_hl_MOUSE_VT200	= 1000,
+	CSI_DEC_hl_ALT_SCREEN	= 1049,
 	CSI_DEC_hl_BRACKETED_PASTE = 2004,
 };
 
@@ -1944,6 +1990,12 @@ static void csi_DEC_hl(struct vc_data *vc, bool on_off)
 		case CSI_DEC_hl_BRACKETED_PASTE:
 			vc->vc_bracketed_paste = on_off;
 			break;
+		case CSI_DEC_hl_ALT_SCREEN:
+			if (on_off)
+				enter_alt_screen(vc);
+			else
+				leave_alt_screen(vc);
+			break;
 		}
 }
 
@@ -2182,6 +2234,13 @@ static void reset_terminal(struct vc_data *vc, int do_clear)
 	vc->vc_deccm		= global_cursor_default;
 	vc->vc_decim		= 0;
 
+	if (vc->vc_saved_screen != NULL) {
+		kfree(vc->vc_saved_screen);
+		vc->vc_saved_screen = NULL;
+		vc->vc_saved_rows = 0;
+		vc->vc_saved_cols = 0;
+	}
+
 	vt_reset_keyboard(vc->vc_num);
 
 	vc->vc_cursor_type = cur_default;
diff --git a/include/linux/console_struct.h b/include/linux/console_struct.h
index 59b4fec5f..f9aabc3cf 100644
--- 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;
+	unsigned int	vc_saved_cols;
+	unsigned int	vc_saved_rows;
 	/* additional information is in vt_kern.h */
 };
 
-- 
2.50.1

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

[Jiri Slaby]

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@grenoble-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

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

[Calixte Pernot]

Hi, thanks for your response.

On 8/25/25 07:47, Jiri Slaby wrote:
> 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@grenoble-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? 

Yes. The 2 functions I added are called by csi_DEC_hl, itself protected 
by console_lock.

console_lock() is called in do_con_write, and the call stack looks like 
this:

do_con_write -> do_con_trol -> csi_DEC -> csi_DEC_hl -> 
enter/leave_alt_screen

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

To be honest I used the same flags as vc->vc_screenbuf, but after 
"reading the F-ing manual", this seems unappropriate here.

"GFP_KERNEL implies GFP_RECLAIM, which means that direct reclaim may be 
triggered under memory pressure; the calling context must be allowed to 
sleep"

I guess we are allowed to sleep here (please correct me if i'm wrong), 
so GFP_KERNEL must be more appropriate.

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

Thanks for the review, I'll rewrite the patch with the suggested changes 
and send it back.

[PATCH v2] vt: add support for smput/rmput escape codes

[Calixte Pernot]

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@grenoble-inp.org>
---
 drivers/tty/vt/vt.c            | 58 ++++++++++++++++++++++++++++++++++
 include/linux/console_struct.h |  3 ++
 2 files changed, 61 insertions(+)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 62049ceb3..bda2a6f76 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -141,6 +141,7 @@ static const struct consw *con_driver_map[MAX_NR_CONSOLES];
 static int con_open(struct tty_struct *, struct file *);
 static void vc_init(struct vc_data *vc, int do_clear);
 static void gotoxy(struct vc_data *vc, int new_x, int new_y);
+static void restore_cur(struct vc_data *vc);
 static void save_cur(struct vc_data *vc);
 static void reset_terminal(struct vc_data *vc, int do_clear);
 static void con_flush_chars(struct tty_struct *tty);
@@ -1344,6 +1345,10 @@ struct vc_data *vc_deallocate(unsigned int currcons)
 		kfree(vc->vc_screenbuf);
 		vc_cons[currcons].d = NULL;
 	}
+	if (vc->vc_saved_screen != NULL) {
+		kfree(vc->vc_saved_screen);
+		vc->vc_saved_screen = NULL;
+	}
 	return vc;
 }
 
@@ -1878,6 +1883,45 @@ 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 */
+	vc->vc_saved_screen = kmemdup((u16 *)vc->vc_origin, size, GFP_KERNEL);
+	if (vc->vc_saved_screen == NULL)
+		return;
+	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);
+	u16 *src, *dest;
+
+	if (vc->vc_saved_screen == NULL)
+		return; /* Not inside an alt-screen */
+	for (unsigned int r = 0; r < rows; r++) {
+		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;
+}
+
 enum {
 	CSI_DEC_hl_CURSOR_KEYS	= 1,	/* CKM: cursor keys send ^[Ox/^[[x */
 	CSI_DEC_hl_132_COLUMNS	= 3,	/* COLM: 80/132 mode switch */
@@ -1888,6 +1932,7 @@ enum {
 	CSI_DEC_hl_MOUSE_X10	= 9,
 	CSI_DEC_hl_SHOW_CURSOR	= 25,	/* TCEM */
 	CSI_DEC_hl_MOUSE_VT200	= 1000,
+	CSI_DEC_hl_ALT_SCREEN	= 1049,
 	CSI_DEC_hl_BRACKETED_PASTE = 2004,
 };
 
@@ -1944,6 +1989,12 @@ static void csi_DEC_hl(struct vc_data *vc, bool on_off)
 		case CSI_DEC_hl_BRACKETED_PASTE:
 			vc->vc_bracketed_paste = on_off;
 			break;
+		case CSI_DEC_hl_ALT_SCREEN:
+			if (on_off)
+				enter_alt_screen(vc);
+			else
+				leave_alt_screen(vc);
+			break;
 		}
 }
 
@@ -2182,6 +2233,13 @@ static void reset_terminal(struct vc_data *vc, int do_clear)
 	vc->vc_deccm		= global_cursor_default;
 	vc->vc_decim		= 0;
 
+	if (vc->vc_saved_screen != NULL) {
+		kfree(vc->vc_saved_screen);
+		vc->vc_saved_screen = NULL;
+		vc->vc_saved_rows = 0;
+		vc->vc_saved_cols = 0;
+	}
+
 	vt_reset_keyboard(vc->vc_num);
 
 	vc->vc_cursor_type = cur_default;
diff --git a/include/linux/console_struct.h b/include/linux/console_struct.h
index 59b4fec5f..13b35637b 100644
--- 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 */
+	u16		*vc_saved_screen;
+	unsigned int	vc_saved_cols;
+	unsigned int	vc_saved_rows;
 	/* additional information is in vt_kern.h */
 };
 
-- 
2.50.1