[Qemu-devel] [PATCH 0/3] qed: Add support for zero clusters

[Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>]

This patch series adds zero data clusters to QED.  Clusters can be marked as
zero clusters to store zeroed regions in a space-efficient way.  The patch
never actually creates new zero clusters but includes the I/O path support code
to handle them if they are used by an image file.

Image streaming and copy-on-read take advantage of zero data clusters to avoid
expanding out zeroes from the backing file.  Those features are separate
patches that will come later but I'm presenting this patch now so we can get
this core QED image format feature in before doing the first QEMU release
containing QED.

The first patch fixes up an issue with the QED merge where '^' characters were
dropped from the QED specification.

The last two patches document and implement zero clusters, which were
originally implemented by Anthony Liguori <aliguori@us.ibm.com>.