Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754856Ab0BAWJR (ORCPT ); Mon, 1 Feb 2010 17:09:17 -0500 Received: from mail-px0-f189.google.com ([209.85.216.189]:51901 "EHLO mail-px0-f189.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752442Ab0BAWJP (ORCPT ); Mon, 1 Feb 2010 17:09:15 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:content-transfer-encoding :in-reply-to:user-agent; b=K4/tL+CE4Z1iDX8ZrAXbef/d83j0c+f+zqUSE5Rb9nDqJf8ONdf0D71cI4sl6OL8pw PRnjrhmZbmZ6Bp3APeB5X4SGmpfv4WTQ30R773SdwBsIDDCowG8Vk0k26zKI2HgvoO0m ycJzt8IGfQ+uyH59ZN1z5wQYXGDRZMj7/bTNg= Date: Mon, 1 Feb 2010 14:08:56 -0800 From: Dmitry Torokhov To: John Kacur Cc: Arnd Bergmann , Thadeu Lima de Souza Cascardo , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] input: remove BKL from uinput open function Message-ID: <20100201220856.GB7380@core.coreip.homeip.net> References: <1264800197-29523-1-git-send-email-cascardo@holoscopio.com> <201001302257.09354.arnd@arndb.de> <520f0cf11001301507k20e3cf8dqa73026e12f3a1767@mail.gmail.com> <201001310520.55813.arnd@arndb.de> <20100131052942.GA12320@core.coreip.homeip.net> <520f0cf11002011222h134dbf06rf1db612da9a9728@mail.gmail.com> <520f0cf11002011227s74e57673j3922941f7ee87989@mail.gmail.com> <20100201212132.GA7380@core.coreip.homeip.net> <520f0cf11002011350u3b541a0cxfb0ed882dca13afe@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <520f0cf11002011350u3b541a0cxfb0ed882dca13afe@mail.gmail.com> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5023 Lines: 129 On Mon, Feb 01, 2010 at 10:50:25PM +0100, John Kacur wrote: > On Mon, Feb 1, 2010 at 10:21 PM, Dmitry Torokhov > wrote: > > On Mon, Feb 01, 2010 at 09:27:22PM +0100, John Kacur wrote: > >> On Mon, Feb 1, 2010 at 9:22 PM, John Kacur wrote: > >> > On Sun, Jan 31, 2010 at 6:29 AM, Dmitry Torokhov > >> > wrote: > >> >> On Sun, Jan 31, 2010 at 05:20:55AM +0100, Arnd Bergmann wrote: > >> >>> On Sunday 31 January 2010, John Kacur wrote: > >> >>> > > Sorry, I should have been clearer, but not implementing llseek > >> >>> > > is the problem I was referring to: When a driver has no explicit > >> >>> > > .llseek operation in its file operations and does not call > >> >>> > > nonseekable_open from its open operation, the VFS layer will > >> >>> > > implicitly use default_llseek, which takes the BKL. We're > >> >>> > > in the process of changing drivers not to do this, one by one > >> >>> > > so we can kill the BKL in the end. > >> >>> > > > >> >>> > > >> >>> > I know we've discussed this before, but why wouldn't the following > >> >>> > make more sense? > >> >>> > ?.llseek ? ? ? ? = no_llseek, > >> >>> > >> >>> That's one of the possible solutions. Assigning it to generic_file_llseek > >> >>> also gets rid of the BKL but keeps the current behaviour (calling seek > >> >>> returns success without having an effect, no_llseek returns -ESPIPE), > >> >>> while calling nonseekable_open has the other side-effect of making > >> >>> pread/pwrite fail with -ESPIPE, which is more consistent than > >> >>> only failing seek. > >> >>> > >> >> > >> >> OK, so how about the patch below (on top of Thadeu's patch)? > >> >> > >> >> -- > >> >> Dmitry > >> >> > >> >> Input: uinput - use nonseekable_open > >> >> > >> >> Seeking does not make sense for uinput so let's use nonseekable_open > >> >> to mark the device non-seekable. > >> >> > >> >> Signed-off-by: Dmitry Torokhov > >> >> --- > >> >> > >> >> ?drivers/input/misc/uinput.c | ? ?7 +++++++ > >> >> ?1 files changed, 7 insertions(+), 0 deletions(-) > >> >> > >> >> > >> >> diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c > >> >> index 18206e1..7089151 100644 > >> >> --- a/drivers/input/misc/uinput.c > >> >> +++ b/drivers/input/misc/uinput.c > >> >> @@ -278,6 +278,7 @@ static int uinput_create_device(struct uinput_device *udev) > >> >> ?static int uinput_open(struct inode *inode, struct file *file) > >> >> ?{ > >> >> ? ? ? ?struct uinput_device *newdev; > >> >> + ? ? ? int error; > >> >> > >> >> ? ? ? ?newdev = kzalloc(sizeof(struct uinput_device), GFP_KERNEL); > >> >> ? ? ? ?if (!newdev) > >> >> @@ -291,6 +292,12 @@ static int uinput_open(struct inode *inode, struct file *file) > >> >> > >> >> ? ? ? ?file->private_data = newdev; > >> >> > >> >> + ? ? ? error = nonseekable_open(inode, file); > >> >> + ? ? ? if (error) { > >> >> + ? ? ? ? ? ? ? kfree(newdev); > >> >> + ? ? ? ? ? ? ? return error; > >> >> + ? ? ? } > >> >> + > >> >> ? ? ? ?return 0; > >> >> ?} > >> >> > >> >> > >> > > >> > Hmnn, if you look at nonseekable_open() it will always return 0. I > >> > think you can just do the following. > > > > It always returns 0 _now_ but I do not see any guarantees that it will > > never ever return anything but 0. If somebody would provide such > > garantee then we certainly would not need to handle errors. > > Well, all it's doing is changing the f_mode. If anyone ever changes > that function > to return anything other than 0 it will be their responsibility to go > fix all the > uses of it. No, not really. > If you do a git grep of nonseekable_open, you'll see that this > is a very common paradigm. (to return 0). The reason for nonseekable_open return 0 is so that you can plug it directly into fsops. The fact that many users abuse that and do: return nonseekable_open(indoe, file); when doing: nonseekable_open(indoe, file); return 0; would not introduce any complexity if they dont want to handle errors at this time, and would be much safer (and one could mark nonseekable_open() __must_check down the road if it is ever changed to actually fail), does not validate such practice in any way. > It makes your code shorter, > and more readable. Plus, you are writing speculative code based on > what might exist in the future? No, I try to write the code that handles errors from functions that could return errors even if current implementation does not do that. > Also, then should uinput_release be called? > If it is called will kfree be called twice on the same memory. If it > isn't called, is > that a problem because you've already done most of the work that requires > a call to uinput_destroy_device ? Why would release be called if open failed? -- Dmitry -- 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/