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.
const typeof(*ptr) __val = *(ptr);
And we're good to go (with kerneldoc almost ready for core submission
:P);
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> + *(ptr) = (typeof(*ptr))0; \
> + T__; \
> +})
> +
> #endif
--
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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