Re: [Xen-devel] [PATCH 02/16] x86: fix: make atomic_read() param const

[Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>]

Hi Andrew,

On 7/11/2016 6:18 PM, Andrew Cooper wrote:
> On 09/07/16 05:12, Corneliu ZUZU wrote:
> > This wouldn't let me make a param of a function that used atomic_read() const.
> >
> > Signed-off-by: Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>
> This is a good improvement, but you must make an identical adjustment to
> the arm code, otherwise you will end up with subtle build failures.
Right, didn't even realize it was X86-specific.

> If you are really feeling up to it, having a common xen/atomic.h with
>
> typedef struct { int counter; } atomic_t;
> #define ATOMIC_INIT(i) { (i) }
>
> and some prototypes such as:
>
> static inline int atomic_read(const atomic_t *v);
>
> would be great, but this looks like it has the possibility to turn into
> a rats nest.  If it does, then just doubling up this code for arm is ok.
>
> ~Andrew
Yes, that might be more complicated than we expect and I don't know if 
making code such as this common would be a good idea, usually these 
functions are always architecture-specific. It might be better to keep 
them separate - they don't add much anyway since their implementation is 
short - than risk unexpected different behavior on a future arch. But 
then again I don't know much details of their implementation, so anyway, 
I'd surely prefer to do this kind of change in a separate patch.
> > ---
> >   xen/include/asm-x86/atomic.h | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/xen/include/asm-x86/atomic.h b/xen/include/asm-x86/atomic.h
> > index d246b70..0b250c8 100644
> > --- a/xen/include/asm-x86/atomic.h
> > +++ b/xen/include/asm-x86/atomic.h
> > @@ -94,7 +94,7 @@ typedef struct { int counter; } atomic_t;
> >    *
> >    * Atomically reads the value of @v.
> >    */
> > -static inline int atomic_read(atomic_t *v)
> > +static inline int atomic_read(const atomic_t *v)
> >   {
> >       return read_atomic(&v->counter);
> >   }
> > @@ -105,7 +105,7 @@ static inline int atomic_read(atomic_t *v)
> >    *
> >    * Non-atomically reads the value of @v
> >    */
> > -static inline int _atomic_read(atomic_t v)
> > +static inline int _atomic_read(const atomic_t v)
> >   {
> >       return v.counter;
> >   }
Thanks,
Zuzu C.

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