linux-kernel - Re: [PATCH v9 4/4] console: Make persistent scrollback a boot parameter

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Message-ID: <1484170890.1301.8.camel@gmx.de>
Date:   Wed, 11 Jan 2017 22:41:30 +0100
From:   Manuel Schölling <manuel.schoelling@....de>
To:     Adam Borowski <kilobyte@...band.pl>
Cc:     gregkh@...uxfoundation.org, jslaby@...e.com, lkml14@...tdoyle.com,
        rdunlap@...radead.org, shorne@...il.com, andrey_utkin@...tmail.com,
        akpm@...ux-foundation.org, paul.burton@...tec.com,
        daniel.vetter@...ll.ch, tj@...nel.org, hdegoede@...hat.com,
        linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org
Subject: 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@....de>
> > Suggested-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.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