linux-kernel - Re: [PATCH 2/8] PM: suspend_block: Add driver to access suspend blockers from user-space

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Date:	Wed, 26 May 2010 13:06:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Florian Mickler <florian@...kler.org>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Randy Dunlap <rdunlap@...otime.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>,
	Jim Collar <jim.collar@...are.net>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Avi Kivity <avi@...hat.com>, Len Brown <len.brown@...el.com>,
	Pavel Machek <pavel@....cz>, Magnus Damm <damm@...l.co.jp>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Nigel Cunningham <nigel@...onice.net>,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH 2/8] PM: suspend_block: Add driver to access suspend 
 blockers from user-space

On Wed, 2010-05-26 at 12:51 +0200, Florian Mickler wrote:
> On Wed, 26 May 2010 03:47:27 -0700
> Arve Hjønnevåg <arve@...roid.com> wrote:
> 
> > 2010/5/26 Peter Zijlstra <peterz@...radead.org>:
> > > On Fri, 2010-05-21 at 15:46 -0700, Arve Hjønnevåg wrote:
> > >> +To create a suspend blocker from user space, open the suspend_blocker
> > >> special
> > >> +device file:
> > >> +
> > >> +    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
> > >> +
> > >> +then optionally call:
> > >> +
> > >> +    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
> > >> +
> > >> +To activate the suspend blocker call:
> > >> +
> > >> +    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
> > >> +
> > >> +To deactivate it call:
> > >> +
> > >> +    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
> > >> +
> > >> +To destroy the suspend blocker, close the device:
> > >> +
> > >> +    close(fd);
> > >
> > > Urgh, please let the open() be BLOCK, the close() be UNBLOCK, and keep
> > > the SET_NAME thing if you really care.
> > >
> > 
> > That would be very inefficient.
> > 
> 
> Also I think it is intended to enforce named suspend blockers. (For
> debugging/accounting purposes).

I don't think the code as proposed mandates you SET_NAME, and I didn't
propose killing that off, you can still SET_NAME after you open() and
acquire the thing.

Anyway, the whole point is moot since its simply not needed at all.
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