Re: [Qemu-devel] [PATCH v11 1/7] bitmap: fix bitmap_count_one

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Wei Wang (wei.w.wang@intel.com) wrote:
> BITMAP_LAST_WORD_MASK(nbits) returns 0xffffffff when "nbits=0", which
> makes bitmap_count_one fail to handle the "nbits=0" case. It appears to be
> preferred to remain BITMAP_LAST_WORD_MASK identical to the kernel
> implementation that it is ported from.
> 
> So this patch fixes bitmap_count_one to handle the nbits=0 case.

OK; it's a little odd that it's only bitmap_count_one that's being fixed
for this case; but OK.


Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> Inital Discussion Link:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg554316.html
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> CC: Juan Quintela <quintela@redhat.com>
> CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
> CC: Peter Xu <peterx@redhat.com>
> ---
>  include/qemu/bitmap.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h
> index 509eedd..679f1bd 100644
> --- a/include/qemu/bitmap.h
> +++ b/include/qemu/bitmap.h
> @@ -221,6 +221,10 @@ static inline int bitmap_intersects(const unsigned long *src1,
>  
>  static inline long bitmap_count_one(const unsigned long *bitmap, long nbits)
>  {
> +    if (unlikely(!nbits)) {
> +        return 0;
> +    }
> +
>      if (small_nbits(nbits)) {
>          return ctpopl(*bitmap & BITMAP_LAST_WORD_MASK(nbits));
>      } else {
> -- 
> 1.8.3.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK