Re: [Qemu-devel] [PATCH 14/20] hbitmap: add hbitmap_alloc_with_data and hbitmap_required_size

[Paolo Bonzini <pbonzini@redhat.com>]

Il 17/12/2012 18:14, Eric Blake ha scritto:
> On 12/12/2012 06:46 AM, Paolo Bonzini wrote:
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>>  hbitmap.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++----------
>>  hbitmap.h | 25 +++++++++++++++++++++++++
>>  2 files changed, 72 insertions(+), 10 deletions(-)
> 
> When using hbitmap_alloc_with_data, must the user pass in all 0 data, or
> do you do a one-time slow pass over the passed-in data to populate the
> remaining layers of the hbitmap to allow faster traversal later?

Right, I should add such a pass.

Paolo

>> +HBitmap *hbitmap_alloc_with_data(uint64_t size, int granularity, void *data)
>> +{
>> +    HBitmap *hb = g_malloc0(sizeof(struct HBitmap));
>> +    unsigned i;
>> +
>> +    hb->size = hbitmap_round_size(size, granularity);
>>      hb->granularity = granularity;
>> +    hb->last_level_allocated = (data == NULL);
>> +
>>      for (i = HBITMAP_LEVELS; i-- > 0; ) {
>> -        size = MAX((size + BITS_PER_LONG - 1) >> BITS_PER_LEVEL, 1);
>> -        hb->levels[i] = g_malloc0(size * sizeof(unsigned long));
>> +        if (data == NULL) {
>> +            data = g_malloc0(hbitmap_required_size(size, granularity));
>> +        }
>> +        hb->levels[i] = data;
>> +        data = NULL;
>> +        granularity += BITS_PER_LEVEL;
>>      }
>>  
>>      /* We necessarily have free bits in level 0 due to the definition
>>       * of HBITMAP_LEVELS, so use one for a sentinel.  This speeds up
>>       * hbitmap_iter_skip_words.
>>       */
>> -    assert(size == 1);
>> +    assert(hbitmap_required_size(size, granularity) == sizeof(unsigned long));
>>      hb->levels[0][0] |= 1UL << (BITS_PER_LONG - 1);
>>      return hb;
>>  }
> 
> Based on the implementation, you aren't inspecting the contents of data.
> 
>> +/**
>> + * hbitmap_alloc_with_data:
>> + * @size: Number of bits in the bitmap.
>> + * @granularity: Granularity of the bitmap.
>> + * @data: Pointer to a data block that will be used for the bottom level
>> + * of the HBitmap.
>> + *
>> + * Allocate a new HBitmap, using a client-provided data block for the
>> + * actual bitmap and allocating memory only for the compressed levels.
>> + * If @data is NULL, this function is equivalent to @hbitmap_alloc.
>> + */
>> +HBitmap *hbitmap_alloc_with_data(uint64_t size, int granularity, void *data);
> 
> But this documentation didn't mention that the caller must pass in all 0s.
>