On Thu, 2017-01-19 at 14:23 +0100, Greg KH wrote: > 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 <[email protected]> > > Reviewed-by: Andrey Utkin <[email protected]> > > Tested-by: Andrey Utkin <[email protected]> > > Tested-by: Adam Borowski <[email protected]> > > --- > > 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 ?
Well, clear_console() just switches from one console to another and back again. It just assumes that the scrollback buffer is flushed when switching. My plan is to make a patch for clear_console() as soon as these patches are in the kernel - it's chicken-and-egg problem. Bye, Manuel
