Re: [PATCH v7 15/32] qcow2: Add qcow2_get_subcluster_range_type()

[Eric Blake]

On 5/25/20 1:08 PM, Alberto Garcia wrote:
> There are situations in which we want to know how many contiguous
> subclusters of the same type there are in a given cluster. This can be
> done by simply iterating over the subclusters and repeatedly calling
> qcow2_get_subcluster_type() for each one of them.
>
> However once we determined the type of a subcluster we can check the
> rest efficiently by counting the number of adjacent ones (or zeroes)
> in the bitmap. This is what this function does.
>
> Signed-off-by: Alberto Garcia <address@hidden>
> ---
>   block/qcow2-cluster.c | 51 +++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 51 insertions(+)

> +    if (*type == QCOW2_SUBCLUSTER_INVALID) {
> +        return -EINVAL;
> +    } else if (!has_subclusters(s) || *type == QCOW2_SUBCLUSTER_COMPRESSED) {
> +        return s->subclusters_per_cluster - sc_from;
> +    }
> +
> +    switch (*type) {
> +    case QCOW2_SUBCLUSTER_NORMAL:
> +        val = l2_bitmap | QCOW_OFLAG_SUB_ALLOC_RANGE(0, sc_from);
> +        return cto32(val) - sc_from;

Slick.

Reviewed-by: Eric Blake <address@hidden>

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org