Re: [Qemu-devel] Different type of qcow2_get_cluster_type

[lampahome]

>
>
> Both values correspond to L2 entries with bit 0 set.  However,
> QCOW2_CLUSTER_ZERO_ALLOC is an entry that has a non-zero value in bits 9-55
> (the cluster has an allocated host location, we guarantee that things read
> as zero regardless of whether the host data actually contains zeroes at
> that offset, and writes go directly to that offset with no further
> allocation required); while QCOW2_CLUSTER_ZERO_PLAIN is an entry with all
> zeros in bits 9-55 (we guarantee things read as zero, but writes have to
> allocate a new cluster because we have not reserved any space in the host
> yet).
>

If I let one entry called l2_addr of l2 table is 1(also the
QCOW2_CLUSTER_ZERO_PLAIN)
to make it as discard.

After I run qemu-img commit image, and the l2_addr also commit to its
backing file.

But I saw the same entry l2_addr of l2 table in backing file doesn't show
1, and write corresponding cluster with zero.

Is that normal?