Re: [patch 143/166] preadv/pwritev: Add preadv and pwritev system calls.

["H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>]

Linus Torvalds wrote:
> 
> Grr. That may make sense on 32-bit architectures, but makes no sense 
> what-so-ever on 64-bit ones.
> 
> Why not just say that it's two "unsigned long" arguments, and split it by 
> "sizeof unsigned long". And then, on 64-bit architectures, the high bits 
> can be ignored. You can even get gcc to optimize it all away by doing 
> something like
> 
> 	#define HALF_LONG (BITS_IN_LONG / 2)
> 
> 	offset = (((loff_t)high << HALF_LONG) << HALF_LONG) | low;
> 
> and then gcc should automaticaly notice that shifting up that way is just 
> a fancy way of saying "0", and ignore the high bits.
> 
> How married are people to this crazy 2x "32 bits" model?
> 

I certainly am *not* happy with it, and said so when it was first
posted.  My main complaint with it is that it introduces yet another
special case in the kernel<->userspace ABI, because although we've had
this problem before, it has been hacked around a different way every time.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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