svn commit: r321920 - head/sys/sys

[Konstantin Belousov]

On Sat, Aug 05, 2017 at 12:26:03PM +1000, Bruce Evans wrote:
> > +#define	minor(x)	((int)(x))
> 
> Another nice simplification.  Strictly, it should be (int)(dev_t)(x) since
> the pseudo-prototype says that the arg is converted to dev_t, but yesterday
> I couldn't see any differences even for exotic x and exotic arches.
> 
> Today I can see some difference for exotic x and perverse implementations.
> E.g., x with extra bits in a large signed integer type to invoke
> implementation-defined behaviour, and a perverse implementation that
> truncates to 0 for direct conversion to int but does the right thing
> for indirect conversion).  But we depend on the implementation doing
> the right thing for other casts to int.
> 
> Also, if dev_t == uintptr_t, it is valid for the caller to keep dev_t's
> in void *'s internally but not to pass void * to minor() or major()
> according to the prototype.  However, casting in the macros breaks the
> warning for this.  I think pure macros should not cast their args or
> pretend to have prototypes, but require callers to pass args of supported
> types.  The old dev_t macros were closer to this -- they have expressions
> like ((x) << 8) which will fail if x is not an integral type or give
> wrong results ix x has extra bits.
So you are arguing to keep the & 0xffffffff operation ?
I think this is not needed, since your note about cast being equivalent
holds for all supported architectures and I do not see anywhere a contract
for the operations to work on non-dev_t.

So are you fine with the posted patch to sys/types.h ?