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Re: [PATCH v3 2/2] posix: Implement preadv2 and pwritev2

On 06/03/2017 01:04 PM, H.J. Lu wrote:
> On Sat, Jun 3, 2017 at 1:22 AM, Andreas Schwab <schwab@linux-m68k.org> wrote:
>> On Jun 02 2017, "H.J. Lu" <hjl.tools@gmail.com> wrote:
>>
>>> The x86-64 LO_HI_LONG can't be used for p{readv,writev}{64}v2.  Add a
>>> new macro, LO_HI_LONG_FLAGS, to pass the off{64}_t and flags arguments.
>>
>> Why can't LO_HI_LONG just pass the padding unconditionally on x86_64?
>>
> 
> To avoid the unnecessary (long) (((uint64_t) (val)) >> 32).

I think the question is why you can't define it like this:

   (val), 0

?  Are you concerned about the additional overhead of passing that
unnecessary zero at the end of the parameter list for other system
calls?  Or would this result in an observable kernel interface
difference and break stuff?

Thanks,
Florian
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