Re: + separate-atomic_t-declaration-from-asm-atomich-into-asm-atomic_defh.patch added to -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 29 Aug 2008 17:34:16 -0600
Matthew Wilcox <matthew@wil.cx> wrote:

> 
> I see you're fixing up the original patch without commenting on this at
> all.

Sob.  I'm just slogging away trying to get my tree to compile.

One more build error and I drop it all.

> On Fri, Aug 22, 2008 at 03:36:25PM -0600, Matthew Wilcox wrote:
> > On Fri, Aug 22, 2008 at 01:56:38PM -0700, akpm@linux-foundation.org wrote:
> > > Subject: Separate atomic_t declaration from asm/atomic.h into asm/atomic_def.h
> > > From: Huang Ying <ying.huang@intel.com>
> > > 
> > > asm/atomic.h contains both declaration and implementation of atomic_t.  So
> > > there are some implementation related files included in asm/atomic.h.  And
> > > atomic_t is a typedef.  Combination of above makes it impossible to use
> > > atomic_t in files included by atomic.h.  Such as atomic_t can not be used
> > > in linux/kernel.h on i386, because it is included by asm/atomic.h.
> > > 
> > > It is reasonable to separate declaration from implementation.  So a new
> > > file atomic_def.h is added for every architecture to accommodate the
> > > declaration of atomic_t.
> > 
> > Seems to me like all architectures could use:
> > 
> > +++ include/linux/atomic_type.h
> > +typedef struct { volatile int counter; } atomic_t;
> > +#ifdef CONFIG_64BIT
> > +typedef struct { volatile long counter; } atomic64_t;
> > +#endif
> > 
> > S390 has an __aligned__((4)) on theirs -- is this really necessary?
> > Doesn't s390 align ints to 4 bytes automatically?  If it doesn't, it
> > shouldn't be harmful to add it to other architectures (iirc m68k only
> > requires 2-byte alignment for ints ... hmm, wonder if their atomic_t is
> > really atomic if, say, it cross a page boundary ...)
> > 

Sounds right to me.