Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753252Ab0DXOoq (ORCPT ); Sat, 24 Apr 2010 10:44:46 -0400 Received: from netrider.rowland.org ([192.131.102.5]:59572 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752998Ab0DXOoo (ORCPT ); Sat, 24 Apr 2010 10:44:44 -0400 Date: Sat, 24 Apr 2010 10:44:43 -0400 (EDT) From: Alan Stern X-X-Sender: stern@netrider.rowland.org To: Pavel Machek cc: Arve Hj?nnev?g , Len Brown , , , Jesse Barnes , Magnus Damm , Subject: Re: [linux-pm] [PATCH 2/9] PM: suspend_block: Add driver to access suspend blockers from user-space In-Reply-To: <20100424055523.GC2290@elf.ucw.cz> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2523 Lines: 67 On Sat, 24 Apr 2010, Pavel Machek wrote: > On Fri 2010-04-23 20:20:47, Arve Hj?nnev?g wrote: > > On Fri, Apr 23, 2010 at 9:43 AM, Alan Stern wrote: > > > On Fri, 23 Apr 2010, Pavel Machek 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. > > >> > > > >> > Signed-off-by: Arve Hj??nnev??g > > >> > > >> > --- a/Documentation/power/suspend-blockers.txt > > >> > +++ b/Documentation/power/suspend-blockers.txt > > >> > @@ -95,3 +95,20 @@ if (list_empty(&state->pending_work)) > > >> > ?else > > >> > ? ? suspend_block(&state->suspend_blocker); > > >> > > > >> > +User-space API > > >> > +============== > > >> > + > > >> > +To create a suspend_blocker from user-space, open the suspend_blocker device: > > >> > + ? ?fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC); > > >> > +then call: > > >> > + ? ?ioctl(fd, SUSPEND_BLOCKER_IOCTL_INIT(strlen(name)), name); > > >> > > >> > > >> This seems like very wrong idea -- it uses different ioctl number for > > >> each length AFAICT. > > > > > > How about specifying the name by an ordinary write() call instead of > > > by an ioctl()? > > > > > > > I prefer using ioctls. We have three operations at the moment. Init, > > block and unblock. If we do init with write but block and unblock > > using ioctls, it would be pretty strange. Specifying a command and > > Why would it be "strange"? Why indeed? Using write() is the natural way to pass a data buffer into the kernel, especially a variable-length buffer. Mixing ioctl() and write() might seem strange at first, but it has plenty of precedent. Consider adjusting the settings for a serial port, for example. > > argument in a string to write is more complicated to parse than using > > ioctls. > > More complicated to parse? It shouldn't be -- especially if you assume that the init action must always come first. The first write would contain the suspend blocker's name; all following writes would have to be either "on" or "off". That's not hard to parse. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/