Re: [Xen-devel] [PATCH 1/2] asm/atomic.h: common prototyping (add xen/atomic.h)

[Julien Grall <julien.grall@xxxxxxx>]

Hi Corneliu,

On 13/07/2016 12:23, Corneliu ZUZU wrote:
> Following Andrew Cooper's suggestion, create a common-side <xen/atomic.h> to
> establish, among others, prototypes of atomic functions called from common-code.
> Done to avoid introducing inconsistencies between arch-side <asm/atomic.h>
> headers when we make subtle changes to one of them.
>
> Some arm-side macros had to be turned into inline functions in the process.
You forgot to mention that you moved the code from 
asm-arm/arm{32,64}/atomic.h to asm-arm/arm.h.
Furthermore, this change should really be a separate patch.

> Also includes a minor adjustment asm-x86/atomic.h: reorder atomic_inc_and_test()
> to follow after atomic_inc().
>
> Signed-off-by: Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>
[...]

> diff --git a/xen/include/asm-arm/atomic.h b/xen/include/asm-arm/atomic.h
> index 29ab265..8e8c5d1 100644
> --- a/xen/include/asm-arm/atomic.h
> +++ b/xen/include/asm-arm/atomic.h
> @@ -2,6 +2,7 @@
>  #define __ARCH_ARM_ATOMIC__
>
>  #include <xen/config.h>
> +#include <xen/atomic.h>
>  #include <xen/prefetch.h>
>  #include <asm/system.h>
>
> @@ -95,15 +96,6 @@ void __bad_atomic_size(void);
>      default: __bad_atomic_size(); break;                                \
>      }                                                                   \
>  })
> -
> -/*
> - * NB. I've pushed the volatile qualifier into the operations. This allows
> - * fast accessors such as _atomic_read() and _atomic_set() which don't give
> - * the compiler a fit.
> - */
> -typedef struct { int counter; } atomic_t;
> -
> -#define ATOMIC_INIT(i) { (i) }
>
>  /*
>   * On ARM, ordinary assignment (str instruction) doesn't clear the local
> @@ -138,6 +130,85 @@ static inline void _atomic_set(atomic_t *v, int i)
>  # error "unknown ARM variant"
>  #endif
>
> +#define atomic_inc_return(v)    (atomic_add_return(1, v))
> +#define atomic_dec_return(v)    (atomic_sub_return(1, v))
> +
> +/**
> + * atomic_sub_and_test - subtract value from variable and test result
> + * @i: integer value to subtract
> + * @v: pointer of type atomic_t
> + *
> + * Atomically subtracts @i from @v and returns
> + * true if the result is zero, or false for all
> + * other cases.
> + */
> +static inline int atomic_sub_and_test(int i, atomic_t *v)
> +{
> +    return 0 == atomic_sub_return(i, v);
> +}
Please don't use yoda condition. It's less readable and compiler have 
safety nowadays to prevent using "=".
> +
> +/**
> + * atomic_inc - increment atomic variable
> + * @v: pointer of type atomic_t
> + *
> + * Atomically increments @v by 1.
> + */
> +static inline void atomic_inc(atomic_t *v)
> +{
> +    atomic_add(1, v);
> +}
Regards,


--
Julien Grall

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