[libvirt] [PATCH v2 2/3] util: Clear unused part of the map in virBitmapShrink

[Peter Krempa]

On Fri, Feb 02, 2018 at 14:04:31 +0100, Martin Kletzander wrote:
> Some of the other functions depend on the fact that unused bits and longs are
> always zero and it's less error-prone to clear it than fix the other functions.
> It's enough to zero out one piece of the map since we're calling realloc() to
> get rid of the rest (and updating map_len).
> 
> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1540817
> 
> Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
> ---
>  src/conf/domain_conf.c |  4 +++-
>  src/util/virbitmap.c   | 30 ++++++++++++++++++++++--------
>  src/util/virbitmap.h   |  2 +-
>  src/util/virresctrl.c  |  3 ++-
>  tests/virbitmaptest.c  |  8 ++++++++
>  5 files changed, 36 insertions(+), 11 deletions(-)
> 
> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index 01d168eb875b..e827b2a810f7 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -18453,7 +18453,9 @@ virDomainCachetuneDefParse(virDomainDefPtr def,
>  
>      /* We need to limit the bitmap to number of vCPUs.  If there's nothing left,
>       * then we can just clean up and return 0 immediately */
> -    virBitmapShrink(vcpus, def->maxvcpus);
> +    if (virBitmapShrink(vcpus, def->maxvcpus) < 0)
> +        goto cleanup;
> +
>      if (virBitmapIsAllClear(vcpus)) {
>          ret = 0;
>          goto cleanup;
> diff --git a/src/util/virbitmap.c b/src/util/virbitmap.c
> index b2c5c7a6a5ac..33cae2f30569 100644
> --- a/src/util/virbitmap.c
> +++ b/src/util/virbitmap.c
> @@ -1201,21 +1201,35 @@ virBitmapSubtract(virBitmapPtr a,
>  /**
>   * virBitmapShrink:
>   * @map: Pointer to bitmap
> - * @b: last bit position to be excluded from bitmap
> + * @b: Size to reduce the bitmap to
>   *
> - * Resizes the bitmap so that no more than @b bits will fit into it.  Nothing
> - * will change if the size is already smaller than @b.
> - *
> - * NB: Does not adjust the map->map_len so that a subsequent virBitmapExpand
> - * doesn't necessarily need to reallocate.
> + * Reduces the bitmap to size @b.  Nothing will change if the size is already
> + * smaller than or equal to @b.
>   */
> -void
> +int
>  virBitmapShrink(virBitmapPtr map,
>                  size_t b)
>  {
> +    size_t nl = 0;
> +    size_t nb = 0;
> +
>      if (!map)
> -        return;
> +        return 0;
>  
>      if (map->max_bit >= b)
>          map->max_bit = b;
> +
> +    nl = map->max_bit / VIR_BITMAP_BITS_PER_UNIT;
> +    nb = map->max_bit % VIR_BITMAP_BITS_PER_UNIT;
> +    map->map[nl] &= ((1UL << nb) - 1);
> +
> +    nl++;
> +    if (nl == map->map_len)
> +        return 0;
> +
> +    if (VIR_REALLOC_N(map->map, nl) < 0)

With VIR_SHRINK_N you can avoid the return value ;)

ACK
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