On 05/30/2016 06:58 AM, Pavel Butsykin wrote:
>
> Sorry, but it seems this will never happen, because the second write
> will not pass this check:
>
> uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
> uint64_t offset,
> int compressed_size)
> {
> ...
> /* Compression can't overwrite anything. Fail if the cluster was
> already
> * allocated. */
> cluster_offset = be64_to_cpu(l2_table[l2_index]);
> if (cluster_offset & L2E_OFFSET_MASK) {
> qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);
> return 0;
> }
> ...
>
> As you can see we can't do the compressed write in the already allocated
> cluster.Umm, doesn't that defeat the point of compression, if every compressed cluster becomes the head of a new cluster? The whole goal of compression is to be able to fit multiple clusters within one. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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