| Message ID | 1532934837-5966-2-git-send-email-wei.w.wang@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | bitmap: some fixes | expand |
On 07/30/2018 03:13 PM, Wei Wang wrote: > This macro was ported from Linux and we've reached an aggreement there > that the corner case "nbits = 0" is not applicable to this macro, because > when "nbits = 0", which means no bits to mask, this macro is expected to > return 0, instead of 0xffffffff. This patch simply adds a comment above > the macro as a note to users about the corner case. > > Signed-off-by: Wei Wang <wei.w.wang@intel.com> > CC: Dr. David Alan Gilbert <dgilbert@redhat.com> > CC: Juan Quintela <quintela@redhat.com> > CC: Peter Xu <peterx@redhat.com> > --- > include/qemu/bitmap.h | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h > index 509eedd..f53c640 100644 > --- a/include/qemu/bitmap.h > +++ b/include/qemu/bitmap.h > @@ -60,6 +60,7 @@ > */ > > #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1))) > +/* "nbits = 0" is not applicable to this macro. Callers should avoid that. */ > #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1))) > > #define DECLARE_BITMAP(name,bits) \ A better fix would be to directly change the macro to: nbits ? (~0UL >> (-(nbits) & (BITS_PER_LONG - 1))) : 0, so that we don't need to fix other callers like bitmap_full, bitmap_intersects. So just post this out for a discussion whether it's preferred to just adding note comments as we did for linux or fixing the macro directly. Best, Wei
Wei Wang <wei.w.wang@intel.com> wrote: > On 07/30/2018 03:13 PM, Wei Wang wrote: >> This macro was ported from Linux and we've reached an aggreement there >> that the corner case "nbits = 0" is not applicable to this macro, because >> when "nbits = 0", which means no bits to mask, this macro is expected to >> return 0, instead of 0xffffffff. This patch simply adds a comment above >> the macro as a note to users about the corner case. >> >> Signed-off-by: Wei Wang <wei.w.wang@intel.com> >> CC: Dr. David Alan Gilbert <dgilbert@redhat.com> >> CC: Juan Quintela <quintela@redhat.com> >> CC: Peter Xu <peterx@redhat.com> >> --- >> include/qemu/bitmap.h | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h >> index 509eedd..f53c640 100644 >> --- a/include/qemu/bitmap.h >> +++ b/include/qemu/bitmap.h >> @@ -60,6 +60,7 @@ >> */ >> #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & >> (BITS_PER_LONG - 1))) >> +/* "nbits = 0" is not applicable to this macro. Callers should avoid that. */ >> #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1))) >> #define DECLARE_BITMAP(name,bits) \ > > A better fix would be to directly change the macro to: nbits ? (~0UL >>> (-(nbits) & (BITS_PER_LONG - 1))) : 0, > so that we don't need to fix other callers like bitmap_full, > bitmap_intersects. > > So just post this out for a discussion whether it's preferred to just > adding note comments as we did for linux or fixing the macro directly. > > Best, > Wei On one hand: a - we have copied it form linux, we don't want to diverge On the other hand: b - it is much easier to use if we change the macro So, it is a tought one. I slightly preffer b), but will not object to a either. As you are the one doing the patch, your choice. Later, Juan.
On 07/30/2018 09:19 PM, Juan Quintela wrote: > Wei Wang <wei.w.wang@intel.com> wrote: >> On 07/30/2018 03:13 PM, Wei Wang wrote: >>> This macro was ported from Linux and we've reached an aggreement there >>> that the corner case "nbits = 0" is not applicable to this macro, because >>> when "nbits = 0", which means no bits to mask, this macro is expected to >>> return 0, instead of 0xffffffff. This patch simply adds a comment above >>> the macro as a note to users about the corner case. >>> >>> Signed-off-by: Wei Wang <wei.w.wang@intel.com> >>> CC: Dr. David Alan Gilbert <dgilbert@redhat.com> >>> CC: Juan Quintela <quintela@redhat.com> >>> CC: Peter Xu <peterx@redhat.com> >>> --- >>> include/qemu/bitmap.h | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h >>> index 509eedd..f53c640 100644 >>> --- a/include/qemu/bitmap.h >>> +++ b/include/qemu/bitmap.h >>> @@ -60,6 +60,7 @@ >>> */ >>> #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & >>> (BITS_PER_LONG - 1))) >>> +/* "nbits = 0" is not applicable to this macro. Callers should avoid that. */ >>> #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1))) >>> #define DECLARE_BITMAP(name,bits) \ >> A better fix would be to directly change the macro to: nbits ? (~0UL >>>> (-(nbits) & (BITS_PER_LONG - 1))) : 0, >> so that we don't need to fix other callers like bitmap_full, >> bitmap_intersects. >> >> So just post this out for a discussion whether it's preferred to just >> adding note comments as we did for linux or fixing the macro directly. >> >> Best, >> Wei > On one hand: > a - we have copied it form linux, we don't want to diverge > On the other hand: > b - it is much easier to use if we change the macro > > So, it is a tought one. > > I slightly preffer b), but will not object to a either. As you are the > one doing the patch, your choice. Thanks Juan. I plan to choose b - fixing the macro directly. Best, Wei
diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h index 509eedd..f53c640 100644 --- a/include/qemu/bitmap.h +++ b/include/qemu/bitmap.h @@ -60,6 +60,7 @@ */ #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1))) +/* "nbits = 0" is not applicable to this macro. Callers should avoid that. */ #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1))) #define DECLARE_BITMAP(name,bits) \
This macro was ported from Linux and we've reached an aggreement there that the corner case "nbits = 0" is not applicable to this macro, because when "nbits = 0", which means no bits to mask, this macro is expected to return 0, instead of 0xffffffff. This patch simply adds a comment above the macro as a note to users about the corner case. Signed-off-by: Wei Wang <wei.w.wang@intel.com> CC: Dr. David Alan Gilbert <dgilbert@redhat.com> CC: Juan Quintela <quintela@redhat.com> CC: Peter Xu <peterx@redhat.com> --- include/qemu/bitmap.h | 1 + 1 file changed, 1 insertion(+)