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[PATCH v9 4/4] console: Make persistent scrollback a boot parameter

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  [PATCH v9 4/4] console: Make persistent scrollback a boot parameter Manuel Schölling <manuel.schoelling@gmx.de> - 2017-01-10 22:40 +0100
    Re: [PATCH v9 4/4] console: Make persistent scrollback a boot  parameter Adam Borowski <kilobyte@angband.pl> - 2017-01-11 00:10 +0100
      Re: [PATCH v9 4/4] console: Make persistent scrollback a boot  parameter Manuel Schölling <manuel.schoelling@gmx.de> - 2017-01-11 22:50 +0100
      Re: [PATCH v9 4/4] console: Make persistent scrollback a boot  parameter Manuel Schölling <manuel.schoelling@gmx.de> - 2017-01-13 21:10 +0100
        Re: [PATCH v9 4/4] console: Make persistent scrollback a boot  parameter Greg KH <gregkh@linuxfoundation.org> - 2017-01-14 08:30 +0100

#1555931 — [PATCH v9 4/4] console: Make persistent scrollback a boot parameter

The impact of the persistent scrollback feature on the code size is
rather small, so the config option is removed. The feature stays
disabled by default and can be enabled by using the boot command line
parameter 'vgacon.scrollback_persistent=1' or by setting
VGACON_SOFT_SCROLLBACK_PERSISTENT_ENABLE_BY_DEFAULT=y.

Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>
Suggested-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
---
 drivers/video/console/Kconfig  | 12 +++++++-----
 drivers/video/console/vgacon.c | 25 ++++++++++++-------------
 2 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index f500e58f7636..5b71bd905a60 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -47,14 +47,16 @@ config VGACON_SOFT_SCROLLBACK_SIZE
 	  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"
+config VGACON_SOFT_SCROLLBACK_PERSISTENT_ENABLE_BY_DEFAULT
+	bool "Persistent Scrollback History for each console by default"
 	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.
+	  Say Y here if the scrollback history should persist by default when
+	  switching between consoles. Otherwise, the scrollback history will be
+	  flushed each time the console is switched. This feature can also be
+	  enabled using the boot command line parameter
+	  'vgacon.scrollback_persistent=1'.
 
 	  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)
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index ca23d222e029..45a76972495b 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -174,11 +174,9 @@ struct vgacon_scrollback_info {
 };
 
 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 bool scrollback_persistent = \
+	IS_ENABLED(CONFIG_VGACON_SOFT_SCROLLBACK_PERSISTENT_ENABLE_BY_DEFAULT);
 
 static void vgacon_scrollback_reset(int vc_num, size_t reset_size)
 {
@@ -213,20 +211,19 @@ static void vgacon_scrollback_init(int vc_num)
 
 static void vgacon_scrollback_switch(int vc_num)
 {
-#ifndef CONFIG_VGACON_SOFT_SCROLLBACK_PERSISTENT
-	vc_num = 0;
-#endif
+	if (!scrollback_persistent)
+		vc_num = 0;
 
 	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;
+		if (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
+			vgacon_scrollback_reset(vc_num, size);
+		}
 	}
 }
 
@@ -1423,4 +1420,6 @@ const struct consw vga_con = {
 };
 EXPORT_SYMBOL(vga_con);
 
+module_param_named(scrollback_persistent, scrollback_persistent, bool, 0000);
+MODULE_PARM_DESC(scrollback_persistent, "Enable persistent scrollback for all vga consoles");
 MODULE_LICENSE("GPL");
-- 
2.11.0

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#1555991 — Re: [PATCH v9 4/4] console: Make persistent scrollback a boot parameter

On Tue, Jan 10, 2017 at 10:28:38PM +0100, Manuel Schölling wrote:
> The impact of the persistent scrollback feature on the code size is
> rather small, so the config option is removed. The feature stays
> disabled by default and can be enabled by using the boot command line
> parameter 'vgacon.scrollback_persistent=1' or by setting
> VGACON_SOFT_SCROLLBACK_PERSISTENT_ENABLE_BY_DEFAULT=y.
> 
> Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>
> Suggested-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

> +module_param_named(scrollback_persistent, scrollback_persistent, bool, 0000);
> +MODULE_PARM_DESC(scrollback_persistent, "Enable persistent scrollback for all vga consoles");

A command-line knob settable by the end-user is something more persistent
than a config option.  As you're going to extend this code beyond vgacon in
the near future, perhaps it'd be better to have a shared setting for all
console drivers?


Meow!
-- 
Autotools hint: to do a zx-spectrum build on a pdp11 host, type:
  ./configure --host=zx-spectrum --build=pdp11

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#1556962 — Re: [PATCH v9 4/4] console: Make persistent scrollback a boot parameter

On Tue, 2017-01-10 at 23:58 +0100, Adam Borowski wrote:
> On Tue, Jan 10, 2017 at 10:28:38PM +0100, Manuel Schölling wrote:
> > The impact of the persistent scrollback feature on the code size is
> > rather small, so the config option is removed. The feature stays
> > disabled by default and can be enabled by using the boot command
> > line
> > parameter 'vgacon.scrollback_persistent=1' or by setting
> > VGACON_SOFT_SCROLLBACK_PERSISTENT_ENABLE_BY_DEFAULT=y.
> > 
> > Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>
> > Suggested-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> > +module_param_named(scrollback_persistent, scrollback_persistent,
> > bool, 0000);
> > +MODULE_PARM_DESC(scrollback_persistent, "Enable persistent
> > scrollback for all vga consoles");
> 
> A command-line knob settable by the end-user is something more
> persistent
> than a config option.  As you're going to extend this code beyond
> vgacon in
> the near future, perhaps it'd be better to have a shared setting for
> all
> console drivers?
Probably a good idea, but I'm struggling with the implementation a bit:

I tried to run 

  if (strstr(boot_command_line, "nopersistentscrollback")) {...}

in vgacon_scrollback_startup() but I am getting 

  WARNING: modpost: Found 2 section mismatch(es).

when compiling. Probably because vgacon_scrollback_startup() is
executed after init.

I tried to find another way to implement a boot cmd line parameter but
had no luck.
If you/somebody could point me in the right direction, it would be very
much appreciated.

Thanks!

Manuel

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#1558719 — Re: [PATCH v9 4/4] console: Make persistent scrollback a boot parameter

On Tue, 2017-01-10 at 23:58 +0100, Adam Borowski wrote:
> On Tue, Jan 10, 2017 at 10:28:38PM +0100, Manuel Schölling wrote:
> > The impact of the persistent scrollback feature on the code size is
> > rather small, so the config option is removed. The feature stays
> > disabled by default and can be enabled by using the boot command
> > line
> > parameter 'vgacon.scrollback_persistent=1' or by setting
> > VGACON_SOFT_SCROLLBACK_PERSISTENT_ENABLE_BY_DEFAULT=y.
> > 
> > Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>
> > Suggested-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> > +module_param_named(scrollback_persistent, scrollback_persistent,
> > bool, 0000);
> > +MODULE_PARM_DESC(scrollback_persistent, "Enable persistent
> > scrollback for all vga consoles");
> 
> A command-line knob settable by the end-user is something more
> persistent
> than a config option.  As you're going to extend this code beyond
> vgacon in
> the near future, perhaps it'd be better to have a shared setting for
> all
> console drivers?
According to the guys at #kernelnewbies on IRC everybody hates new
command line options.
I'd rather stick to the module parameter for now and maybe introduce a 
new cmd line option later, once this feature has been implemented in
several console drivers.

Bye,

Manuel

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#1558863 — Re: [PATCH v9 4/4] console: Make persistent scrollback a boot parameter

On Fri, Jan 13, 2017 at 09:00:34PM +0100, Manuel Schölling wrote:
> On Tue, 2017-01-10 at 23:58 +0100, Adam Borowski wrote:
> > On Tue, Jan 10, 2017 at 10:28:38PM +0100, Manuel Schölling wrote:
> > > The impact of the persistent scrollback feature on the code size is
> > > rather small, so the config option is removed. The feature stays
> > > disabled by default and can be enabled by using the boot command
> > > line
> > > parameter 'vgacon.scrollback_persistent=1' or by setting
> > > VGACON_SOFT_SCROLLBACK_PERSISTENT_ENABLE_BY_DEFAULT=y.
> > > 
> > > Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>
> > > Suggested-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> > > +module_param_named(scrollback_persistent, scrollback_persistent,
> > > bool, 0000);
> > > +MODULE_PARM_DESC(scrollback_persistent, "Enable persistent
> > > scrollback for all vga consoles");
> > 
> > A command-line knob settable by the end-user is something more
> > persistent
> > than a config option.  As you're going to extend this code beyond
> > vgacon in
> > the near future, perhaps it'd be better to have a shared setting for
> > all
> > console drivers?
> According to the guys at #kernelnewbies on IRC everybody hates new
> command line options.

That was me, you can use my name here :)

> I'd rather stick to the module parameter for now and maybe introduce a 
> new cmd line option later, once this feature has been implemented in
> several console drivers.

Yes, that should be fine.

thanks,

greg k-h

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