Re: [PATCH v2 06/12] range: Introduce range_inverse_array()

[Eric Auger]

Hi Alex,

On 9/19/23 18:29, Alex Williamson wrote:
> On Wed, 13 Sep 2023 10:01:41 +0200
> Eric Auger <eric.auger@redhat.com> wrote:
>
>> This helper reverses an array of regions, turning original
>> regions into holes and original holes into actual regions,
>> covering the whole UINT64_MAX span.
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>
>> ---
>>
>> v1 -> v2:
>> - Move range_inverse_array description comment in the header
>> - Take low/high params
>> ---
>>  include/qemu/range.h |  8 ++++++++
>>  util/range.c         | 45 ++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 53 insertions(+)
>>
>> diff --git a/include/qemu/range.h b/include/qemu/range.h
>> index 7e2b1cc447..2b59e3bf0c 100644
>> --- a/include/qemu/range.h
>> +++ b/include/qemu/range.h
>> @@ -219,4 +219,12 @@ static inline int ranges_overlap(uint64_t first1, 
>> uint64_t len1,
>>  
>>  GList *range_list_insert(GList *list, Range *data);
>>  
>> +/*
>> + * Inverse an array of sorted ranges over the [low, high] span, ie.
>> + * original ranges becomes holes in the newly allocated inv_ranges
>> + */
>> +void range_inverse_array(uint32_t nr_ranges, Range *ranges,
>> +                         uint32_t *nr_inv_ranges, Range **inv_ranges,
>> +                         uint64_t low, uint64_t high);
>> +
>>  #endif
>> diff --git a/util/range.c b/util/range.c
>> index 098d9d2dc0..4baeb588cc 100644
>> --- a/util/range.c
>> +++ b/util/range.c
>> @@ -70,3 +70,48 @@ GList *range_list_insert(GList *list, Range *data)
>>  
>>      return list;
>>  }
>> +
>> +void range_inverse_array(uint32_t nr_ranges, Range *ranges,
>> +                         uint32_t *nr_inv_ranges, Range **inv_ranges,
>> +                         uint64_t low, uint64_t high)
> Rare be it for me to suggest GLib, but we already appear to have
> range_list_insert() making use of GList for an ordered list of Ranges.
> Doesn't this function become a lot easier if we take a sorted GList,
> walk it to create the inverse, and return a new GList of the inverted
> Ranges?  Seems the initial sorted GList would be created by making use
> of the existing range_list_insert() function.  Thanks,

I am not sure this greatly simplifies. This definitively removes the
realloc stuff. But to me what complexifies the algo is the low/high
parameter support instead of hardcoding thel to 0/UINT64_MAX (suggestion
by Philippe which I can understand for such helper though). You can see
the diff with

20230904080451.424731-7-eric.auger@redhat.com/">https://lore.kernel.org/all/20230904080451.424731-7-eric.auger@redhat.com/

I will further look at your suggestion though

Eric
>
> Alex
>
>> +{
>> +    Range *resv;
>> +    int i = 0, j = 0;
>> +
>> +    resv = g_malloc0_n(nr_ranges + 1, sizeof(Range));
>> +
>> +    for (; j < nr_ranges  && (range_upb(&ranges[j]) < low); j++) {
>> +        continue; /* skip all ranges below mon */
>> +    }
>> +
>> +    if (j == nr_ranges) {
>> +        range_set_bounds(&resv[i++], low, high);
>> +        goto realloc;
>> +    }
>> +
>> +    /* first range lob is greater than min, insert a first range */
>> +    if (range_lob(&ranges[j]) > low) {
>> +        range_set_bounds(&resv[i++], low,
>> +                         MIN(range_lob(&ranges[j]) - 1, high));
>> +    }
>> +
>> +    /* insert a range inbetween each original range until we reach max */
>> +    for (; j < nr_ranges - 1; j++) {
>> +        if (range_lob(&ranges[j]) >= high) {
>> +            goto realloc;
>> +        }
>> +        if (range_compare(&ranges[j], &ranges[j + 1])) {
>> +            range_set_bounds(&resv[i++], range_upb(&ranges[j]) + 1,
>> +                             MIN(range_lob(&ranges[j + 1]) - 1, high));
>> +        }
>> +    }
>> +    /* last range upb is less than max, insert a last range */
>> +    if (range_upb(&ranges[j]) <  high) {
>> +        range_set_bounds(&resv[i++],
>> +                          range_upb(&ranges[j]) + 1, high);
>> +    }
>> +realloc:
>> +    *nr_inv_ranges = i;
>> +    resv = g_realloc(resv, i * sizeof(Range));
>> +    *inv_ranges = resv;
>> +}