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From: Greg KH <gregkh@linuxfoundation.org>
To: "Manuel Schölling" <manuel.schoelling@gmx.de>
Cc: jslaby@suse.com, kilobyte@angband.pl, lkml14@scotdoyle.com,
	rdunlap@infradead.org, shorne@gmail.com,
	andrey_utkin@fastmail.com, akpm@linux-foundation.org,
	paul.burton@imgtec.com, daniel.vetter@ffwll.ch, tj@kernel.org,
	hdegoede@redhat.com, linux-kernel@vger.kernel.org,
	linux-fbdev@vger.kernel.org
Subject: Re: [PATCH v10 3/4] console: Add persistent scrollback buffers for all VGA consoles
Date: Thu, 19 Jan 2017 17:33:14 +0100	[thread overview]
Message-ID: <20170119163314.GD22777@kroah.com> (raw)
In-Reply-To: <1484842335.1250.7.camel@gmx.de>

On Thu, Jan 19, 2017 at 05:12:15PM +0100, Manuel Schölling wrote:
> 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 <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 ?
> 
> 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.

I'd recommend that patch get to clear_console() first, having it use the
new escape sequence, if it isn't supported, shouldn't cause any
problems, right?

thanks,

greg k-h

  reply	other threads:[~2017-01-19 16:46 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-04 10:53 [PATCH v7 0/3] " Manuel Schölling
2016-12-04 10:53 ` [PATCH v7 1/3] console: Move scrollback data into its own struct Manuel Schölling
2016-12-04 10:53 ` [PATCH v7 2/3] console: Add callback to flush scrollback buffer to consw struct Manuel Schölling
2016-12-04 10:53 ` [PATCH v7 3/3] console: Add persistent scrollback buffers for all VGA consoles Manuel Schölling
2016-12-06 10:02 ` [PATCH v7 0/3] " Greg KH
2016-12-06 16:32   ` Manuel Schölling
2016-12-21 16:37 ` [PATCH RESEND " Manuel Schölling
2016-12-21 16:37   ` [PATCH RESEND v7 1/3] console: Move scrollback data into its own struct Manuel Schölling
2016-12-21 16:37   ` [PATCH RESEND v7 2/3] console: Add callback to flush scrollback buffer to consw struct Manuel Schölling
2016-12-21 16:37   ` [PATCH RESEND v7 3/3] console: Add persistent scrollback buffers for all VGA consoles Manuel Schölling
2017-01-04 13:54   ` [PATCH RESEND v7 0/3] " Andrey Utkin
2017-01-05 11:33     ` [PATCH v8 " Manuel Schölling
2017-01-05 11:33     ` [PATCH v8 1/3] console: Move scrollback data into its own struct Manuel Schölling
2017-01-05 11:33     ` [PATCH v8 2/3] console: Add callback to flush scrollback buffer to consw struct Manuel Schölling
2017-01-05 11:33     ` [PATCH v8 3/3] console: Add persistent scrollback buffers for all VGA consoles Manuel Schölling
     [not found]       ` <CGME20170110162224epcas1p2095912fa6b73a1457fa86396149e78e9@epcas1p2.samsung.com>
2017-01-10 16:22         ` Bartlomiej Zolnierkiewicz
     [not found]           ` <CGME20170110164435epcas1p314efb9c6ea3ffb971fce06f3bfaec736@epcas1p3.samsung.com>
2017-01-10 16:44             ` Bartlomiej Zolnierkiewicz
2017-01-10 17:31               ` Manuel Schölling
2017-01-10 21:28               ` [PATCH v9 0/4] " Manuel Schölling
2017-01-10 21:28               ` [PATCH v9 1/4] console: Move scrollback data into its own struct Manuel Schölling
2017-01-10 21:28               ` [PATCH v9 2/4] console: Add callback to flush scrollback buffer to consw struct Manuel Schölling
2017-01-10 21:28               ` [PATCH v9 3/4] console: Add persistent scrollback buffers for all VGA consoles Manuel Schölling
2017-01-10 21:28               ` [PATCH v9 4/4] console: Make persistent scrollback a boot parameter Manuel Schölling
2017-01-10 22:58                 ` Adam Borowski
2017-01-11 21:41                   ` Manuel Schölling
2017-01-13 20:00                   ` Manuel Schölling
2017-01-14  7:26                     ` Greg KH
2017-01-11 13:32                 ` kbuild test robot
2017-01-13 20:07                   ` [PATCH v10 0/4] console: Add persistent scrollback buffers for all VGA consoles Manuel Schölling
2017-01-25 10:55                     ` Greg KH
2017-01-13 20:07                   ` [PATCH v10 1/4] console: Move scrollback data into its own struct Manuel Schölling
2017-01-13 20:07                   ` [PATCH v10 2/4] console: Add callback to flush scrollback buffer to consw struct Manuel Schölling
2017-01-13 20:07                   ` [PATCH v10 3/4] console: Add persistent scrollback buffers for all VGA consoles Manuel Schölling
2017-01-19 13:23                     ` Greg KH
2017-01-19 16:12                       ` Manuel Schölling
2017-01-19 16:33                         ` Greg KH [this message]
2017-01-19 23:04                           ` Adam Borowski
2017-01-20 13:16                             ` Adam Borowski
2017-01-20 13:31                               ` Greg KH
2017-01-20 14:27                                 ` Adam Borowski
2017-01-19 17:20                         ` Adam Borowski
2017-01-13 20:07                   ` [PATCH v10 4/4] console: Make persistent scrollback a boot parameter Manuel Schölling
2017-02-02 20:07                 ` [PATCH v9 " Paul Gortmaker
2017-02-03 16:04                   ` Manuel Schölling
2017-02-03 16:45                     ` Adam Borowski
2017-01-02 14:27 ` [PATCH RESEND v7 0/3] console: Add persistent scrollback buffers for all VGA consoles Manuel Schölling
2017-01-02 14:27   ` [PATCH RESEND v7 1/3] console: Move scrollback data into its own struct Manuel Schölling
2017-01-02 14:27   ` [PATCH RESEND v7 2/3] console: Add callback to flush scrollback buffer to consw struct Manuel Schölling
2017-01-02 14:27   ` [PATCH RESEND v7 3/3] console: Add persistent scrollback buffers for all VGA consoles Manuel Schölling

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