linux-kernel - Re: [PATCH v2] vt: add init_hide parameter to suppress boot output

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Message-ID: <20130220221828.GB23856@xo-6d-61-c0.localdomain>
Date:	Wed, 20 Feb 2013 23:18:28 +0100
From:	Pavel Machek <pavel@....cz>
To:	Andy Ross <andy.ross@...driver.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Jiri Slaby <jslaby@...e.cz>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Len Brown <len.brown@...el.com>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH v2] vt: add init_hide parameter to suppress boot output

On Wed 2013-02-20 14:08:25, Andy Ross wrote:
> On 02/20/2013 12:57 PM, Pavel Machek wrote:
> >I'm sure something creative can be done with fake init that shuts
> >the console up then execs previous init. No need to add more kernel
> >knobs, I'd say.
> 
> Fair enough, but some last words:
> 
> That's argument is the "it's about logging" hypothesis again.  Even if
> it were possible to completely shut up console output (something
> that's awfully hard in the general case when running on PC hardware,
> and IMHO from a developer's perspective not even a good thing), that's

Is it really so hard? ... ... ... I'll comment below.

> not the whole problem.  The framebuffer console initialization does a
> buffer clear and mode set, and that clobbers anything the bootloader
> might have left on the screen prematurely, before userspace is ready
> to throw up its own splash.  Splash screens may be a silly
> requirement, but they're still a requirement.

Ok. "quiet" option already leaves the display as is, including tests on it -
at least in VGA text mode case. Would it make sense to behave the same on
framebuffers you care about?

That patch could be quite accepteble, AFAICT. It does not add a new interface,
just makes framebuffers behave similar way to legacy vga.

And now... how to shut off the logging.

/sbin/init:
chvt 99
cat /share/splash > /dev/fb0
exec /sbin/init

...here you go. No flickering, no distro messages on the screen. You have
to display your splash from /sbin/init, but that should not be bad. Hmm?

> And the suspend console problem is likewise at work: ideally you'd
> like to know, for example, that the panel backlight is off before
> suspending.  But what happens in practice is that the kernel does a VT
> switch to/from console 63 and the backlight wakes up (I'm not going to
> pretend I have this bit completely figured out, but the problem is/was
> real and this patch fixed it by suppressing the console visibility).

I believe someone is already fixing this for suspend. rjw would know more.
Lets treat it as separate problem?

> But at the same time: all that other stuff doesn't quite meet the
> requirements (which in this case are basically "nothing happens
> visually between bootloader handoff and the surfaceflinger splash").
> What you get with that is something like what you get with desktop
> distros: you "mostly" never see the console, except when you do.

I don't know what surfaceflinger splash is; if you can display it from
init (as above) or very soon after that you should be fine.
								Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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