Re: [PATCH v8 3/3] console: Add persistent scrollback buffers for all VGA consoles

[Bartlomiej Zolnierkiewicz]

On Tuesday, January 10, 2017 05:22:22 PM Bartlomiej Zolnierkiewicz wrote:
> 
> Hi,
> 
> The patchset generally looks fine to me but I have a question
> regarding new VGACON_SOFT_SCROLLBACK_PERSISTENT config option.
> 
> Since the code size impact to support the persistent scrollback
> feature is minimal wouldn't it be better to always include it?
> 
> The feature would be disabled by default and could be enabled
> by using the new kernel command line parameter (you may also add
> a new config option for enabling it by default if desired).

Something like:

#ifdef VGACON_SOFT_SCROLLBACK_PERSISTENT_ENABLE_BY_DEFAULT
static bool scrollback_persistent = 1;
#else
static bool scrollback_persistent;
#endif

module_param_named(scrollback_persistent, scrollback_persistent, bool, 0);
MODULE_PARM_DESC(scrollback_persistent, "Enable persistent scrollback feature");

and then use scrollback_persistent variable in vgacon_scrollback_switch()
to control the actual behavior instead of ifdefs.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

> Best regards,
> --
> Bartlomiej Zolnierkiewicz
> Samsung R&D Institute Poland
> Samsung Electronics
> 
> On Thursday, January 05, 2017 12:33:20 PM Manuel Schölling wrote:
> > Add a scrollback buffers for each VGA console. The benefit is that
> > the scrollback history is not flushed when switching between consoles
> > but is persistent.
> > The buffers are allocated on demand when a new console is opened.
> > 
> > This breaks tools like clear_console that rely on flushing the
> > scrollback history by switching back and forth between consoles
> > which is why this feature is disabled by default.
> > Use the escape sequence \e[3J instead for flushing the buffer.
> > 
> > Signed-off-by: Manuel Schölling <manuel.schoelling@xxxxxx>
> > Reviewed-by: Andrey Utkin <andrey_utkin@xxxxxxxxxxxx>
> > Tested-by: Andrey Utkin <andrey_utkin@xxxxxxxxxxxx>
> > Tested-by: Adam Borowski <kilobyte@xxxxxxxxxx>
> > ---
> >  drivers/video/console/Kconfig  |  25 +++++++-
> >  drivers/video/console/vgacon.c | 142 ++++++++++++++++++++++++++---------------
> >  2 files changed, 111 insertions(+), 56 deletions(-)
> > 
> > diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
> > index c3f1fb9ee820..f500e58f7636 100644
> > --- a/drivers/video/console/Kconfig
> > +++ b/drivers/video/console/Kconfig
> > @@ -43,9 +43,28 @@ config VGACON_SOFT_SCROLLBACK_SIZE
> >         range 1 1024
> >         default "64"
> >         help
> > -         Enter the amount of System RAM to allocate for the scrollback
> > -	 buffer.  Each 64KB will give you approximately 16 80x25
> > -	 screenfuls of scrollback buffer
> > +	  Enter the amount of System RAM to allocate for scrollback
> > +	  buffers of VGA consoles. Each 64KB will give you approximately
> > +	  16 80x25 screenfuls of scrollback buffer.
> > +
> > +config VGACON_SOFT_SCROLLBACK_PERSISTENT
> > +	bool "Persistent Scrollback History for each console"
> > +	depends on VGACON_SOFT_SCROLLBACK
> > +	default n
> > +	help
> > +	  Say Y here if the scrollback history should persist when switching
> > +	  between consoles. Otherwise, the scrollback history will be flushed
> > +	  each time the console is switched.
> > +
> > +	  This feature might break your tool of choice to flush the scrollback
> > +	  buffer, e.g. clear(1) will work fine but Debian's clear_console(1)
> > +	  will be broken, which might cause security issues.
> > +	  You can use the escape sequence \e[3J instead if this feature is
> > +	  activated.
> > +
> > +	  Note that a buffer of VGACON_SOFT_SCROLLBACK_SIZE is taken for each
> > +	  created tty device.
> > +	  So if you use a RAM-constrained system, say N here.
> >  
> >  config MDA_CONSOLE
> >  	depends on !M68K && !PARISC && ISA
> > diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
> > index 9a7c2bbc5326..ca23d222e029 100644
> > --- a/drivers/video/console/vgacon.c
> > +++ b/drivers/video/console/vgacon.c
> > @@ -162,7 +162,7 @@ static inline void vga_set_mem_top(struct vc_data *c)
> >  
> >  #ifdef CONFIG_VGACON_SOFT_SCROLLBACK
> >  /* software scrollback */
> > -static struct vgacon_scrollback_info {
> > +struct vgacon_scrollback_info {
> >  	void *data;
> >  	int tail;
> >  	int size;
> > @@ -171,74 +171,110 @@ static struct vgacon_scrollback_info {
> >  	int cur;
> >  	int save;
> >  	int restore;
> > -} vgacon_scrollback;
> > +};
> > +
> > +static struct vgacon_scrollback_info *vgacon_scrollback_cur;
> > +#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_PERSISTENT
> > +static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
> > +#else
> > +static struct vgacon_scrollback_info vgacon_scrollbacks[1];
> > +#endif
> >  
> > -static void vgacon_scrollback_reset(size_t reset_size)
> > +static void vgacon_scrollback_reset(int vc_num, size_t reset_size)
> >  {
> > -	if (vgacon_scrollback.data && reset_size > 0)
> > -		memset(vgacon_scrollback.data, 0, reset_size);
> > +	struct vgacon_scrollback_info *scrollback = &vgacon_scrollbacks[vc_num];
> > +
> > +	if (scrollback->data && reset_size > 0)
> > +		memset(scrollback->data, 0, reset_size);
> >  
> > -	vgacon_scrollback.cnt  = 0;
> > -	vgacon_scrollback.tail = 0;
> > -	vgacon_scrollback.cur  = 0;
> > +	scrollback->cnt  = 0;
> > +	scrollback->tail = 0;
> > +	scrollback->cur  = 0;
> >  }
> >  
> > -static void vgacon_scrollback_init(int pitch)
> > +static void vgacon_scrollback_init(int vc_num)
> >  {
> > -	int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
> > -
> > -	if (vgacon_scrollback.data) {
> > -		vgacon_scrollback.cnt  = 0;
> > -		vgacon_scrollback.tail = 0;
> > -		vgacon_scrollback.cur  = 0;
> > -		vgacon_scrollback.rows = rows - 1;
> > -		vgacon_scrollback.size = rows * pitch;
> > +	int pitch = vga_video_num_columns * 2;
> > +	size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
> > +	int rows = size / pitch;
> > +	void *data;
> > +
> > +	data = kmalloc_array(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE, 1024,
> > +			     GFP_NOWAIT);
> > +
> > +	vgacon_scrollbacks[vc_num].data = data;
> > +	vgacon_scrollback_cur = &vgacon_scrollbacks[vc_num];
> > +
> > +	vgacon_scrollback_cur->rows = rows - 1;
> > +	vgacon_scrollback_cur->size = rows * pitch;
> > +
> > +	vgacon_scrollback_reset(vc_num, size);
> > +}
> > +
> > +static void vgacon_scrollback_switch(int vc_num)
> > +{
> > +#ifndef CONFIG_VGACON_SOFT_SCROLLBACK_PERSISTENT
> > +	vc_num = 0;
> > +#endif
> > +
> > +	if (!vgacon_scrollbacks[vc_num].data) {
> > +		vgacon_scrollback_init(vc_num);
> > +	} else {
> > +#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_PERSISTENT
> > +		vgacon_scrollback_cur = &vgacon_scrollbacks[vc_num];
> > +#else
> > +		size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
> > +
> > +		vgacon_scrollback_reset(vc_num, size);
> > +#endif
> >  	}
> >  }
> >  
> >  static void vgacon_scrollback_startup(void)
> >  {
> > -	vgacon_scrollback.data = kcalloc(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE,
> > -		1024, GFP_NOWAIT);
> > -	vgacon_scrollback_init(vga_video_num_columns * 2);
> > +	vgacon_scrollback_cur = &vgacon_scrollbacks[0];
> > +	vgacon_scrollback_init(0);
> >  }
> >  
> >  static void vgacon_scrollback_update(struct vc_data *c, int t, int count)
> >  {
> >  	void *p;
> >  
> > -	if (!vgacon_scrollback.size || c->vc_num != fg_console)
> > +	if (!vgacon_scrollback_cur->data || !vgacon_scrollback_cur->size ||
> > +	    c->vc_num != fg_console)
> >  		return;
> >  
> >  	p = (void *) (c->vc_origin + t * c->vc_size_row);
> >  
> >  	while (count--) {
> > -		scr_memcpyw(vgacon_scrollback.data + vgacon_scrollback.tail,
> > +		scr_memcpyw(vgacon_scrollback_cur->data +
> > +			    vgacon_scrollback_cur->tail,
> >  			    p, c->vc_size_row);
> > -		vgacon_scrollback.cnt++;
> > +
> > +		vgacon_scrollback_cur->cnt++;
> >  		p += c->vc_size_row;
> > -		vgacon_scrollback.tail += c->vc_size_row;
> > +		vgacon_scrollback_cur->tail += c->vc_size_row;
> >  
> > -		if (vgacon_scrollback.tail >= vgacon_scrollback.size)
> > -			vgacon_scrollback.tail = 0;
> > +		if (vgacon_scrollback_cur->tail >= vgacon_scrollback_cur->size)
> > +			vgacon_scrollback_cur->tail = 0;
> >  
> > -		if (vgacon_scrollback.cnt > vgacon_scrollback.rows)
> > -			vgacon_scrollback.cnt = vgacon_scrollback.rows;
> > +		if (vgacon_scrollback_cur->cnt > vgacon_scrollback_cur->rows)
> > +			vgacon_scrollback_cur->cnt = vgacon_scrollback_cur->rows;
> >  
> > -		vgacon_scrollback.cur = vgacon_scrollback.cnt;
> > +		vgacon_scrollback_cur->cur = vgacon_scrollback_cur->cnt;
> >  	}
> >  }
> >  
> >  static void vgacon_restore_screen(struct vc_data *c)
> >  {
> > -	vgacon_scrollback.save = 0;
> > +	vgacon_scrollback_cur->save = 0;
> >  
> > -	if (!vga_is_gfx && !vgacon_scrollback.restore) {
> > +	if (!vga_is_gfx && !vgacon_scrollback_cur->restore) {
> >  		scr_memcpyw((u16 *) c->vc_origin, (u16 *) c->vc_screenbuf,
> >  			    c->vc_screenbuf_size > vga_vram_size ?
> >  			    vga_vram_size : c->vc_screenbuf_size);
> > -		vgacon_scrollback.restore = 1;
> > -		vgacon_scrollback.cur = vgacon_scrollback.cnt;
> > +		vgacon_scrollback_cur->restore = 1;
> > +		vgacon_scrollback_cur->cur = vgacon_scrollback_cur->cnt;
> >  	}
> >  }
> >  
> > @@ -252,41 +288,41 @@ static void vgacon_scrolldelta(struct vc_data *c, int lines)
> >  		return;
> >  	}
> >  
> > -	if (!vgacon_scrollback.data)
> > +	if (!vgacon_scrollback_cur->data)
> >  		return;
> >  
> > -	if (!vgacon_scrollback.save) {
> > +	if (!vgacon_scrollback_cur->save) {
> >  		vgacon_cursor(c, CM_ERASE);
> >  		vgacon_save_screen(c);
> > -		vgacon_scrollback.save = 1;
> > +		vgacon_scrollback_cur->save = 1;
> >  	}
> >  
> > -	vgacon_scrollback.restore = 0;
> > -	start = vgacon_scrollback.cur + lines;
> > +	vgacon_scrollback_cur->restore = 0;
> > +	start = vgacon_scrollback_cur->cur + lines;
> >  	end = start + abs(lines);
> >  
> >  	if (start < 0)
> >  		start = 0;
> >  
> > -	if (start > vgacon_scrollback.cnt)
> > -		start = vgacon_scrollback.cnt;
> > +	if (start > vgacon_scrollback_cur->cnt)
> > +		start = vgacon_scrollback_cur->cnt;
> >  
> >  	if (end < 0)
> >  		end = 0;
> >  
> > -	if (end > vgacon_scrollback.cnt)
> > -		end = vgacon_scrollback.cnt;
> > +	if (end > vgacon_scrollback_cur->cnt)
> > +		end = vgacon_scrollback_cur->cnt;
> >  
> > -	vgacon_scrollback.cur = start;
> > +	vgacon_scrollback_cur->cur = start;
> >  	count = end - start;
> > -	soff = vgacon_scrollback.tail - ((vgacon_scrollback.cnt - end) *
> > -					 c->vc_size_row);
> > +	soff = vgacon_scrollback_cur->tail -
> > +		((vgacon_scrollback_cur->cnt - end) * c->vc_size_row);
> >  	soff -= count * c->vc_size_row;
> >  
> >  	if (soff < 0)
> > -		soff += vgacon_scrollback.size;
> > +		soff += vgacon_scrollback_cur->size;
> >  
> > -	count = vgacon_scrollback.cnt - start;
> > +	count = vgacon_scrollback_cur->cnt - start;
> >  
> >  	if (count > c->vc_rows)
> >  		count = c->vc_rows;
> > @@ -300,13 +336,13 @@ static void vgacon_scrolldelta(struct vc_data *c, int lines)
> >  
> >  		count *= c->vc_size_row;
> >  		/* how much memory to end of buffer left? */
> > -		copysize = min(count, vgacon_scrollback.size - soff);
> > -		scr_memcpyw(d, vgacon_scrollback.data + soff, copysize);
> > +		copysize = min(count, vgacon_scrollback_cur->size - soff);
> > +		scr_memcpyw(d, vgacon_scrollback_cur->data + soff, copysize);
> >  		d += copysize;
> >  		count -= copysize;
> >  
> >  		if (count) {
> > -			scr_memcpyw(d, vgacon_scrollback.data, count);
> > +			scr_memcpyw(d, vgacon_scrollback_cur->data, count);
> >  			d += count;
> >  		}
> >  
> > @@ -320,13 +356,13 @@ static void vgacon_flush_scrollback(struct vc_data *c)
> >  {
> >  	size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
> >  
> > -	if (c->vc_num == fg_console)
> > -		vgacon_scrollback_reset(size);
> > +	vgacon_scrollback_reset(c->vc_num, size);
> >  }
> >  #else
> >  #define vgacon_scrollback_startup(...) do { } while (0)
> >  #define vgacon_scrollback_init(...)    do { } while (0)
> >  #define vgacon_scrollback_update(...)  do { } while (0)
> > +#define vgacon_scrollback_switch(...)  do { } while (0)
> >  
> >  static void vgacon_restore_screen(struct vc_data *c)
> >  {
> > @@ -805,7 +841,7 @@ static int vgacon_switch(struct vc_data *c)
> >  			vgacon_doresize(c, c->vc_cols, c->vc_rows);
> >  	}
> >  
> > -	vgacon_scrollback_init(c->vc_size_row);
> > +	vgacon_scrollback_switch(c->vc_num);
> >  	return 0;		/* Redrawing not needed */
> >  }