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

Greg KH
2017-01-19T13:23:52Z

On Fri, Jan 13, 2017 at 09:07:57PM +0100, 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@gmx.de>
> Reviewed-by: Andrey Utkin <andrey_utkin@fastmail.com>
> Tested-by: Andrey Utkin <andrey_utkin@fastmail.com>
> Tested-by: Adam Borowski <kilobyte@angband.pl>
> ---
> 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.

This issue is the one that makes me the most worried. Why doesn't
clear_console() work anymore? Why doesn't it use \e[3J ?

thanks,

greg k-h