On 2/20/20 9:54 AM, Max Reitz wrote:
+Subcluster Allocation Bitmap (for standard clusters):
+
+ Bit 0 - 31: Allocation status (one bit per subcluster)
+
+ 1: the subcluster is allocated. In this case the
+ host cluster offset field must contain a valid
+ offset.
+ 0: the subcluster is not allocated. In this case
+ read requests shall go to the backing file or
+ return zeros if there is no backing file data.
+
+ Bits are assigned starting from the most significant one.
+ (i.e. bit x is used for subcluster 31 - x)
I still prefer it the other way round, both personally (e.g. it’s the C
ordering), and because other places in qcow2 use LSb for bit ordering
(the refcount order).
Internal consistency with refcount order using LSb ordering is the
strongest reason to flip things, and have bit x be subcluster x.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
