linux-kernel - Re: [PATCH] input: remove BKL from uinput open function

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Date:	Sat, 30 Jan 2010 21:29:42 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	John Kacur <jkacur@...il.com>,
	Thadeu Lima de Souza Cascardo <cascardo@...oscopio.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] input: remove BKL from uinput open function

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 <dtor@...l.ru>
---

 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;
 }
 
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