A Practical Look at QEMU and libvirt Block Layer Primitives
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QEMU is an open source machine emulator and virtualizer (most commonly
used with Xen or KVM linux kernel module).  In this talk, we'll focus on
QEMU's block subsystem, which forms the foundation for some of the
essential virtualization storage features -- live disk sychronization,
incremental backups, QCOW2 disk image chains, and point-in-time
snapshots to name a few. These features are driven by an underlying set
of block primitives, which are typically exposed to users via an
external virtualization API, such as libvirt.

We'll walk-through some of these primitives, discuss their invocation --
either directly using QEMU Machine Protocol (QMP) interface or the
libvirt's shell interface (`virsh`). We'll also understand how some of
them could be combined to perform specific useful operations, e.g. live
disk backups; how live storage migration is achieved via a combination
of QEMU's built-in Network Block Device server plus the live disk
synchronization mechanism.  Higher-level cloud infrastructure such as
OpenStack (its Compute project) call into this QEMU block layer via
libvirt APIs.