Re: [PATCH 2/9] PM: suspend_block: Add driver to access suspend blockers from user-space

From: Pavel Machek <pavel@ucw.cz>
To: Arve Hj?nnev?g <arve@android.com>
Cc: ncunningham@crca.org.au, u.luckas@road.de, swetland@google.com,
	linux-pm@lists.linux-foundation.org
Subject: Re: [PATCH 2/9] PM: suspend_block: Add driver to access suspend	blockers from user-space
Date: Thu, 7 May 2009 12:32:50 +0200	[thread overview]
Message-ID: <20090507103249.GA6132@elf.ucw.cz> (raw)
In-Reply-To: <d6200be20905061842l64e71797r11807dff47f335ed@mail.gmail.com>

On Wed 2009-05-06 18:42:59, Arve Hj?nnev?g wrote:
> On Tue, May 5, 2009 at 1:12 PM, Pavel Machek <pavel@ucw.cz> wrote:
> > Hi!
> >
> >> Add a misc device, "suspend_blocker", that allows user-space processes
> >> to block auto suspend. The device has ioctls to create a suspend_blocker,
> >> and to block and unblock suspend. To delete the suspend_blocker, close
> >> the device.
> >
> > Rafael proposed write() interface. I don't think you answered that.
> >
> 
> I think an ioctl interface makes more sense. With a write interface
> you either have to do string parsing, or invent some other protocol
> between the driver and user-space.

Or perhaps just use "userspace/%d" % pid as a name?

1) can't be faked that trivially

2) small / mostly fixed size

3) can use nicer write protocol?

> > kzalloc on user-supplied argument. Sounds like bad idea.
> >
> > Aha. And probably integer overflow in the same line. Ouch.
> >
> 
> The size is limited to _IOC_SIZEMASK with is 13 or 14 bits depending
> on the architecture. Do you want a lower limit on the name length?

16K of unswappable kernel memory for name is a bit too much, yes.

									Pavel
-- 
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