Date: Fri, 23 Jan 2004 16:27:22 +1300
From: Nigel Cunningham <ncunningham@users.sourceforge.net>
Subject: Re: PATCH: Export console functions for	use	by	Software	Suspend	nice
 display
In-reply-to: <1074827571.974.191.camel@gaston>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Daniel Jacobowitz <dan@debian.org>, viro@parcelfarce.linux.theplanet.co.uk,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Reply-to: ncunningham@users.sourceforge.net
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Hi.

On Fri, 2004-01-23 at 16:12, Benjamin Herrenschmidt wrote:
> > Locking is not an issue. This is suspend-to-disk. Everything else is
> > stopped while we're working.
>=20
> No. You can still get a printk from irq...=20

Mmm. But we also adjust the console loglevel depending upon the
verbosity of debugging info required. (And reset it when we're done).
When the nice display is on, the loglevel is 0 or 1. If a driver wants
to printk at KERN_EMERG or KERN_ALERT then, well the display should get
messed up a little :>

> > By the way, am I understanding the suggestion correctly? Do you
> > (collective) mean getting a fd for /dev/console from within kernel code
> > and using that? I've been looking at the way printk works and wondering
> > if con->write is equivalent (once I find the right console to write to)=
?
>=20
> Yes. get an fd and write to it. grep for write to find other uses :)

I did. Didn't find much. I'll look again. Perhaps I'm just blind :>

> You may have to be a bit careful about what context you are in, but I
> suppose it's whatever userland process triggered the sleep in the
> first place, no ? For load, it's probably whatever process did swapon ?

No. There's a kernel daemon - kswsuspd - that does all the hard work.
The userland process that initiates the suspend sleeps in
wait_for_completion until post resume. At boot time, we initiate the
resume via an init call. Still fine?

Regards,

Nigel
.
--=20
My work on Software Suspend is graciously brought to you by
LinuxFund.org.

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