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SubjectRe: [RFC][PATCH resend 8/12] asm-generic: bitops: introduce le bit offset macro
On Tue, 04 May 2010 19:08:23 +0300
Avi Kivity <avi@redhat.com> wrote:

> On 05/04/2010 06:03 PM, Arnd Bergmann wrote:
> > On Tuesday 04 May 2010, Takuya Yoshikawa wrote:
...
> >> So let us use the le bit offset calculation part by defining it as a new
> >> macro: generic_le_bit_offset() .
> >>
> > Does this work correctly if your user space is 32 bits (i.e. unsigned long
> > is different size in user space and kernel) in both big- and little-endian
> > systems?
> >
> > I'm not sure about all the details, but I think you cannot in general share
> > bitmaps between user space and kernel because of this.
> >
>
> That's why the bitmaps are defined as little endian u64 aligned, even on
> big endian 32-bit systems. Little endian bitmaps are wordsize agnostic,
> and u64 alignment ensures we can use long-sized bitops on mixed size
> systems.

There was a suggestion to propose set_le_bit_user() kind of macros.
But what I thought was these have a constraint you two explained and seemed to be
a little bit specific to some area, like KVM.

So I decided to propose just the offset calculation macro.

Thanks, Takuya


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