Linux Virtualization - Oct 2015 - [PATCH] drm/virtio: use %llu format string form atomic64_t

On Wed, Oct 07, 2015 at 01:23:07PM +0200, Arnd Bergmann wrote:
> > I haven't checked all architectures, but I assume what happens is
that
> > 64-bit ones just #define atomic64_t atomic_long_t, so they don't
have
> > to provide three sets of functions.
> 
> scratch that, I just looked at all the architectures and found that
it's
> just completely arbitrary, even within one architecture you get a mix
> of 'long' and 'long long', plus this gem from MIPS:
> 
> static __inline__ int atomic64_add_unless(atomic64_t *v, long a, long u)
> 
> which truncates the result to 32 bit.
Eh...  The result is 0/1 so nothing is truncated.  Alpha, MIPS,
PARISC and PowerPC are using the same prototype and x86 only differs
in the use of inline instead __inline__.  And anyway, that function on
MIPS is only built for CONFIG_64BIT.

What's wrong on MIPS is the comment describing the function's return
value
which was changed by f24219b4e90cf70ec4a211b17fbabc725a0ddf3c (atomic: move
atomic_add_unless to generic code) and I've queued up a patch to fix that
since a few days.  I guess that was a cut and paste error from
__atomic_add_unless which indeed does return the old value.

  Ralf

On Monday 19 October 2015 11:37:00 Ralf Baechle wrote:
> On Wed, Oct 07, 2015 at 01:23:07PM +0200, Arnd Bergmann wrote:
> 
> > > I haven't checked all architectures, but I assume what
happens is that
> > > 64-bit ones just #define atomic64_t atomic_long_t, so they
don't have
> > > to provide three sets of functions.
> > 
> > scratch that, I just looked at all the architectures and found that
it's
> > just completely arbitrary, even within one architecture you get a mix
> > of 'long' and 'long long', plus this gem from MIPS:
> > 
> > static __inline__ int atomic64_add_unless(atomic64_t *v, long a, long
u)
> > 
> > which truncates the result to 32 bit.
> 
> Eh...  The result is 0/1 so nothing is truncated.  Alpha, MIPS,
> PARISC and PowerPC are using the same prototype and x86 only differs
> in the use of inline instead __inline__.  And anyway, that function on
> MIPS is only built for CONFIG_64BIT.
Ah, got it. Sorry about that.
> What's wrong on MIPS is the comment describing the function's
return value
> which was changed by f24219b4e90cf70ec4a211b17fbabc725a0ddf3c (atomic: move
> atomic_add_unless to generic code) and I've queued up a patch to fix
that
> since a few days.  I guess that was a cut and paste error from
> __atomic_add_unless which indeed does return the old value.
Thanks!

	Arnd