Re: [Qemu-devel] [PATCH v2 3/3] bitops: use bool

[Blue Swirl]

On Mon, Jul 9, 2012 at 7:43 AM, Markus Armbruster <address@hidden> wrote:
> address@hidden writes:
>
>> From: Blue Swirl <address@hidden>
>>
>> Use 'bool' type for return value of bit test functions.
>
> Matter of taste.  'bool' makes sense if you think of these functions as
> predicates (ugly ones, with side effects).  'int' makes sense if you
> think of them as returning the bit value (a bit is not a truth value in
> my book).

The documentation actually talks about returning the old value.

But I think the kernel version (with the same documentation) however
returns a truth value:
static inline int test_and_clear_bit(int nr, volatile unsigned long *addr)
{
        int oldbit;

        asm volatile(LOCK_PREFIX "btr %2,%1\n\t"
                     "sbb %0,%0"
                     : "=r" (oldbit), ADDR : "Ir" (nr) : "memory");

        return oldbit;
}

SBB oldbit, oldbit with oldbit = 0 initially and carry set will produce -1, no?

>
> In my opinion, this is just unnecessary churn, and unnecessary deviation
> from established kernel practice.

We use for example NetBSD queue macros with heavy modification. If we
have a need to modify code derived from Linux kernel, we should do it
as well. In this case the kernel practice seems to be inconsistent and
worth fixing.