From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Torokhov Subject: Re: [PATCH] input: remove BKL from uinput open function Date: Mon, 1 Feb 2010 14:08:56 -0800 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-Transfer-Encoding: QUOTED-PRINTABLE Return-path: 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 Content-Disposition: inline In-Reply-To: <520f0cf11002011350u3b541a0cxfb0ed882dca13afe@mail.gmail.com> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: John Kacur Cc: Arnd Bergmann , Thadeu Lima de Souza Cascardo , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org 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 wro= te: > >> > 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 ll= seek > >> >>> > > is the problem I was referring to: When a driver has no ex= plicit > >> >>> > > .llseek operation in its file operations and does not call > >> >>> > > nonseekable_open from its open operation, the VFS layer wi= ll > >> >>> > > 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 fol= lowing > >> >>> > make more sense? > >> >>> > =A0.llseek =A0 =A0 =A0 =A0 =3D 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 (call= ing seek > >> >>> returns success without having an effect, no_llseek returns -E= SPIPE), > >> >>> while calling nonseekable_open has the other side-effect of ma= king > >> >>> 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 > >> >> --- > >> >> > >> >> =A0drivers/input/misc/uinput.c | =A0 =A07 +++++++ > >> >> =A01 files changed, 7 insertions(+), 0 deletions(-) > >> >> > >> >> > >> >> diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/u= input.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 uinp= ut_device *udev) > >> >> =A0static int uinput_open(struct inode *inode, struct file *fil= e) > >> >> =A0{ > >> >> =A0 =A0 =A0 =A0struct uinput_device *newdev; > >> >> + =A0 =A0 =A0 int error; > >> >> > >> >> =A0 =A0 =A0 =A0newdev =3D kzalloc(sizeof(struct uinput_device),= GFP_KERNEL); > >> >> =A0 =A0 =A0 =A0if (!newdev) > >> >> @@ -291,6 +292,12 @@ static int uinput_open(struct inode *inode= , struct file *file) > >> >> > >> >> =A0 =A0 =A0 =A0file->private_data =3D newdev; > >> >> > >> >> + =A0 =A0 =A0 error =3D nonseekable_open(inode, file); > >> >> + =A0 =A0 =A0 if (error) { > >> >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 kfree(newdev); > >> >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return error; > >> >> + =A0 =A0 =A0 } > >> >> + > >> >> =A0 =A0 =A0 =A0return 0; > >> >> =A0} > >> >> > >> >> > >> > > >> > 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 w= ill > > never ever return anything but 0. If somebody would provide such > > garantee then we certainly would not need to handle errors. >=20 > 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 a= t 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 requ= ires > a call to uinput_destroy_device ? Why would release be called if open failed? --=20 Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-input" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html