[RFC][PATCH resend 8/12] asm-generic: bitops: introduce le bit offset macro

Arnd Bergmann arnd at arndb.de
Wed May 5 01:03:00 EST 2010

On Tuesday 04 May 2010, Takuya Yoshikawa wrote:
> Although we can use *_le_bit() helpers to treat bitmaps le arranged,
> having le bit offset calculation as a seperate macro gives us more freedom.
> For example, KVM has le arranged dirty bitmaps for VGA, live-migration
> and they are used in user space too. To avoid bitmap copies between kernel
> and user space, we want to update the bitmaps in user space directly.
> To achive this, le bit offset with *_user() functions help us a lot.
> 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

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.


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