Re: [PATCH v10 3/4] console: Add persistent scrollback buffers for all VGA consoles

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 <redacted>
Reviewed-by: Andrey Utkin <redacted>
Tested-by: Andrey Utkin <redacted>
Tested-by: Adam Borowski <redacted>
---
 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.