On Fri, Aug 12, 2016 at 10:55:46AM +0300, Joonas Lahtinen wrote:
> On pe, 2016-08-12 at 07:54 +0100, Chris Wilson wrote:
> > A simple little macro to clear a pointer and return the old value. This
> > is useful for writing
> >
> > value = *ptr;
> > if (!value)
> > return;
> >
> > *ptr = 0;
> > ...
> > free(value);
> >
> > in a slightly more concise form:
> >
> > value = fetch_and_zero(ptr);
> > if (!value)
> > return;
> >
> > ...
> > free(value);
> >
> > with the idea that this establishes a pattern that may be extended for
> > atomic use (using xchg or cmpxchg) i.e. atomic_fetch_and_zero() and
> > similar to llist.
> >
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/i915_drv.h | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > index a4203ff0cf7f..731c67fc9796 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -3903,4 +3903,10 @@ static inline bool __i915_request_irq_complete(struct drm_i915_gem_request *req)
> > return false;
> > }
> >
> > +#define fetch_and_zero(ptr) ({ \
> > + typeof(*ptr) T__ = *(ptr); \
>
> Looking at container_of etc. it's always __ as prefix.
The advice to use the suffix is from gcc's manual iirc, and there are a
few macros that do dotted around the place, but it looks overwhelmingly
in favour of the prefix.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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