Re: [RFC PATCH V2 00/10] IIO: Use the new cleanup.h magic

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 14 Jan 2024 17:33:36 +0000
Jonathan Cameron <jic23@kernel.org> wrote:

> On Sun, 17 Dec 2023 19:10:48 -0600
> David Lechner <dlechner@baylibre.com> wrote:
> 
> > On Sun, Dec 17, 2023 at 11:36 AM Jonathan Cameron <jic23@kernel.org> wrote:  
> > >
> > > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > >
> > > A lot of the advantages of the automated cleanup added for locks and similar
> > > are not that useful in IIO unless we also deal with the
> > > iio_device_claim_direct_mode() / iio_device_release_direct_mode()
> > > calls that prevent IIO device drivers from transitioning into buffered
> > > mode whilst calls are in flight + prevent sysfs reads and writes from
> > > interfering with buffered capture if it is enabled.
> > >
> > > Relies on Peter Zilstra's conditional cleanup handling which is queued
> > > up for the merge window in the tip tree. This series is based on
> > > a merge of tip/master into iio/togreg.
> > >
> > > All comments welcome. If this looks positive I'll make use of it in a
> > > lot more drivers, but hopefully these give an idea of how it will work.
> > >
> > > The need to always handle what happens after
> > > iio_device_claim_direct_scoped() {} is a little irritating but the
> > > compiler will warn if you don't do it and it's not obvious how to
> > > let the compiler know the magic loop (hidden in the cleanup.h macros)
> > > always runs once.  Example:
> > >
> > >         iio_device_claim_direct_scoped(return -EBUSY, indio_dev) {
> > >                 return 42;
> > >         }
> > >         /* Can't actually get here, but compiler moans if no return val */
> > >         return -EINVAL;    
> > 
> > Maybe better would be?
> > 
> >         unreachable();  
> 
> Interesting thought, but there is very little precedence for using that in the kernel.
> + I think it's a C23 feature so we'd be relying on whether gcc and clang happened
> to implement it rather than being sure it was available.

Ah. I'd missed the default implementation in compiler.h.
So let us fall back on the first argument of limited precedence.

J

> 
> Jonathan
> 
> 
> >   
> > > }    
>