linux-kernel - Re: [linux-pm] driver power operations (was Re: suspend2 merge)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <200704272034.12535.rjw@sisk.pl>
Date:	Fri, 27 Apr 2007 20:34:11 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Johannes Berg <johannes@...solutions.net>,
	Alan Stern <stern@...land.harvard.edu>,
	Nick Piggin <npiggin@...e.de>, Ingo Molnar <mingo@...e.hu>,
	suspend2-devel@...ts.suspend2.net, Mike Galbraith <efault@....de>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Con Kolivas <kernel@...ivas.org>, Adrian Bunk <bunk@...sta.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Pavel Machek <pavel@....cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pm <linux-pm@...ts.linux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [linux-pm] driver power operations (was Re: suspend2 merge)

On Friday, 27 April 2007 17:52, Linus Torvalds wrote:
> 
> On Fri, 27 Apr 2007, Rafael J. Wysocki wrote:
> > 
> > I think we can use 'stages' and pass them as arguments to the functions.
> 
> No, no NOOOO!
> 
> If you use stages, just describe them in the function name instead.	
> 
> > quiesce(PREPARE) -- that may be needed for drivers that allocate much memory
> > before quiescing devices (if any)
> > ...
> > quiesce(PRE_SNAPSHOT)
> > ...
> > quiesce(PRE_SNAPSHOT_IRQ_OFF)
> 
> There is *no* advantage to this (and _lots_ of disadvantages) compared to 
> saying
> 
> 	dev->snapshot_prepare(dev);
> 	dev->snapshot_freeze(dev);
> 	dev->snapshot(dev)
> 
> The latter is
>  - more readable
>  - MUCH easier for programmers to write readable code for (if-statements 
>    and case-statements are *by*definition* more complicated to parse both 
>    for humans and for CPU's - static information is good)
>  - allows for the different stages to have different arguments, and 
>    somewhat related to that, to have better static C type checking.
> 
> Look here, which one is more readable:
> 
> 	int some_mixed_function(int arg)
> 	{
> 		do_one_thing();
> 		if (arg == SLEEP)
> 			do_another_thing();
> 		else
> 			do_yet_another_thing();
> 	}
> 
> or
> 
> 	int do_sleep(void)
> 	{
> 		do_one_thing();
> 		do_another_thing();
> 	}
> 
> 	int prepare_to_sleep(void)
> 	{
> 		do_one_thing();
> 		do_yet_another_thing();
> 	}
> 
> and quite frankly, while the second case may take more lines of code, 
> anybody who says that it's not clearer what it does (because it can 
> "self-document" with function names etc) is either lying, or just a really 
> bad programmer. The second case is also likely faster and probably not 
> larger code-size-wise either, since it does static decisions _statically_ 
> (since all callers are realistically going to use a constant argument 
> anyway, and the argument really is static).
> 
> Finally, the second case is *much* easier to fix, exactly because it 
> doesn't mix up the cases. You can change the arguments, you can have 
> totally different locking, you don't need things like
> 
> 	int gfp = (arg == SLEEP) ? GFP_ATOMIC : GFP_KERNEL;
> 
> etc, and it's just more logical.
> 
> So don't overload a function. That's the *bug* with the current 
> "dev->suspend()" interface already. Don't re-create it. The current one 
> overloads two *totally*different* operations onto one function. 
> 
> Just don't do it. Not in the suspend part, not *ever*.

OK, I won't.

Greetings,
Rafael
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/