On Mon, Feb 01, 2010 at 09:27:22PM +0100, John Kacur wrote:
> On Mon, Feb 1, 2010 at 9:22 PM, John Kacur <jkacur@xxxxxxxxxx> wrote:
> > On Sun, Jan 31, 2010 at 6:29 AM, Dmitry Torokhov
> > <dmitry.torokhov@xxxxxxxxx> 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@xxxxxxx>
> >> ---
> >>
> >> 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.
> >
> > 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@xxxxxxxxxx>
> >
>
> Btw, Thadeu Lima de Souza Cascardo should just combine that all into
> one patch, no point really in making two patches out of that.
I think these are 2 separate changes (the fact that nonseekable_open
also gets rid of BKL invocation is a side-effect), that is not
considering the fact that I already applied Thadeu's change and don't
want to rewind my public branch unless really necessary.
Thanks.
--
Dmitry
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