Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754226Ab0DYWeX (ORCPT ); Sun, 25 Apr 2010 18:34:23 -0400 Received: from mail-gy0-f174.google.com ([209.85.160.174]:48192 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752138Ab0DYWeW convert rfc822-to-8bit (ORCPT ); Sun, 25 Apr 2010 18:34:22 -0400 MIME-Version: 1.0 In-Reply-To: References: <20100424055523.GC2290@elf.ucw.cz> Date: Sun, 25 Apr 2010 15:34:20 -0700 Message-ID: Subject: Re: [linux-pm] [PATCH 2/9] PM: suspend_block: Add driver to access suspend blockers from user-space From: =?ISO-8859-1?Q?Arve_Hj=F8nnev=E5g?= To: Alan Stern Cc: Pavel Machek , Len Brown , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Jesse Barnes , Magnus Damm , linux-pm@lists.linux-foundation.org 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: 3402 Lines: 83 On Sat, Apr 24, 2010 at 7:44 AM, Alan Stern wrote: > 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. > That sound like to opposite situation to me. It uses ioctls for setup and read/write access the data stream. >> > 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. > Why should I have to parse a string at all? We already have a control interface, ioctl, where user space can pass a command with data. If we later want to add other commands we can easily add them without breaking existing command. With your interface, where the first write is a name, adding more initialization data later becomes harder. I also don't like that wring the same string twice has a different meaning the second time. With the ioctl interface, you forget to initialize the suspend blocker, it block and unblock operations will fail. With your interface you create a suspend blocker call "on" or "off". -- Arve Hj?nnev?g -- 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/