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

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Date:	Mon, 1 Feb 2010 21:22:01 +0100
From:	John Kacur <jkacur@...hat.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	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 6:29 AM, Dmitry Torokhov
<dmitry.torokhov@...il.com> 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 <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;
>  }
>
>

Hmnn, if you look at nonseekable_open() it will always return 0. I
think you can just do the following.

diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
index 18206e1..697c0a6 100644
--- a/drivers/input/misc/uinput.c
+++ b/drivers/input/misc/uinput.c
@@ -291,7 +291,7 @@ static int uinput_open(struct inode *inode, struct file *fil

        file->private_data = newdev;

-       return 0;
+       return nonseekable_open(inode, file);
 }

Signed-off-by: John Kacur <jkacur@...hat.com>
--
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