On Mon, 31 Mar 2025, Stefano Stabellini wrote:
> On Mon, 31 Mar 2025, Jan Beulich wrote:
> > On 28.03.2025 00:34, Stefano Stabellini wrote:
> > > --- a/xen/common/bitmap.c
> > > +++ b/xen/common/bitmap.c
> > > @@ -52,7 +52,7 @@ static void clamp_last_byte(uint8_t *bp, unsigned int
> > > nbits)
> > > unsigned int remainder = nbits % 8;
> > >
> > > if (remainder)
> > > - bp[nbits/8] &= (1U << remainder) - 1;
> > > + *bp &= (1U << remainder) - 1;
> > > }
> >
> > Technically there's nothing wrong with dropping the if(), I think. Even more
> > so then than now, ...
We need to keep the if because otherwise we end up zeroing the last
8-bit-aligned byte
> > > @@ -338,7 +338,6 @@ static void bitmap_long_to_byte(uint8_t *bp, const
> > > unsigned long *lp,
> > > nbits -= 8;
> > > }
> > > }
> > > - clamp_last_byte(bp, nbits);
> > > }
> > >
> > > static void bitmap_byte_to_long(unsigned long *lp, const uint8_t *bp,
> > > @@ -363,7 +362,6 @@ static void bitmap_long_to_byte(uint8_t *bp, const
> > > unsigned long *lp,
> > > unsigned int nbits)
> > > {
> > > memcpy(bp, lp, DIV_ROUND_UP(nbits, BITS_PER_BYTE));
> > > - clamp_last_byte(bp, nbits);
> > > }
> >
> > ... with the two prior call sites now shrunk to ...
> >
> > > @@ -384,21 +382,41 @@ int bitmap_to_xenctl_bitmap(struct xenctl_bitmap
> > > *xenctl_bitmap,
> > > uint8_t zero = 0;
> > > int err = 0;
> > > unsigned int xen_bytes = DIV_ROUND_UP(nbits, BITS_PER_BYTE);
> > > - uint8_t *bytemap = xmalloc_array(uint8_t, xen_bytes);
> > > -
> > > - if ( !bytemap )
> > > - return -ENOMEM;
> > > + uint8_t last;
> > >
> > > guest_bytes = DIV_ROUND_UP(xenctl_bitmap->nr_bits, BITS_PER_BYTE);
> > > copy_bytes = min(guest_bytes, xen_bytes);
> > >
> > > - bitmap_long_to_byte(bytemap, bitmap, nbits);
> > > + if ( IS_ENABLED(__BIG_ENDIAN) )
> > > + {
> > > + uint8_t *bytemap = xmalloc_array(uint8_t, xen_bytes);
> > >
> > > - if ( copy_bytes &&
> > > - copy_to_guest(xenctl_bitmap->bitmap, bytemap, copy_bytes) )
> > > - err = -EFAULT;
> > > + if ( !bytemap )
> > > + return -ENOMEM;
> > >
> > > - xfree(bytemap);
> > > + bitmap_long_to_byte(bytemap, bitmap, nbits);
> > > + last = bytemap[nbits / 8];
> > > +
> > > + if ( copy_bytes > 1 &&
> > > + copy_to_guest(xenctl_bitmap->bitmap, bytemap, copy_bytes -
> > > 1) )
> > > + err = -EFAULT;
> > > +
> > > + xfree(bytemap);
> > > + }
> > > + else
> > > + {
> > > + const uint8_t *bytemap = (const uint8_t *)bitmap;
> > > + last = bytemap[nbits / 8];
> > > +
> > > + if ( copy_bytes > 1 &&
> > > + copy_to_guest(xenctl_bitmap->bitmap, bytemap, copy_bytes -
> > > 1) )
> > > + err = -EFAULT;
> > > + }
> > > +
> > > + clamp_last_byte(&last, nbits);
> >
> > ... just one, I wonder if that being a separate function is actually still
> > necessary.
> >
> > As indicated before, I think it would be nice if the two identical copy-out
> > operations could also be folded.
>
> Please see: https://marc.info/?l=xen-devel&m=174319650100975
>
> Other than that, I addressed all the other points
Sorry, that's not true, one comment above
