Release of libvirt-7.6.0

[Jiri Denemark]

The 7.6.0 release of both libvirt and libvirt-python is tagged and
signed tarballs and source RPMs are available at

    https://libvirt.org/sources/
    https://libvirt.org/sources/python/

Thanks everybody who helped with this release by sending patches,
reviewing, testing, or providing any other feedback. Your work is
greatly appreciated.

* Security

  * storage: Unlock pool objects on ACL check failures in ``storagePoolLookupByTargetPath`` (CVE-2021-3667)

    A logic bug in ``storagePoolLookupByTargetPath`` where the storage pool
    object was left locked after a failure of the ACL check could potentially
    deprive legitimate users access to a storage pool object by users who don't
    have access.

* New features

  * qemu: Incremental backup support via ``virDomainBackupBegin``

    libvirt-7.6 along with the unreleased qemu-6.1 will fully support the change
    block tracking features (block-dirty-bitmaps) to be able to do incremental
    backups and management of the checkpoint states via the appropriate APIs.

  * qemu: Add support for launch security type s390-pv

    Specifying s390-pv as launch security type in an s390 domain prepares for
    running the guest in protected virtualization secure mode, also known as
    IBM Secure Execution. This simplifies the definition and reduces the risk
    of an incorrect definition, e.g. by forgetting to specify ``iommu=on`` on
    all virtio devices.

  * domstats: Add haltpolling time statistic interface

    Domstats now provide the data of cpu haltpolling time. This feature relies
    on statistics available after kernel version 5.8. This will allow the user
    to get more accurate CPU usage information if needed.

* Bug fixes

  * qemu: Fix migration with ``VIR_MIGRATE_NON_SHARED_INC``

    libvirt 7.3.0 introduced a bug where ``VIR_MIGRATE_NON_SHARED_INC`` would
    not actually migrate the contents of the disk due to broken logic and at
    the same time could trigger migration of storage when
    ``VIR_MIGRATE_TUNNELLED`` is requested. This release fixes the bug.

  * qemu: Don't emit ``VIR_DOMAIN_EVENT_ID_BLOCK_THRESHOLD`` twice when registered with index

    When registering the threshold event with the index notation (e.g.
    ``vda[3]``) libvirt would emit the event also for ``vda`` if the image is
    in the top layer. The intention was to emit two events only when the
    original registration was done without the index.

  * qemu: Pass discard requests for disks with ``copy_on_read='on'``

    When a disk using the ``copy_on_read='on'`` option is configured also with
    ``discard='unmap'`` the discard requests will now be passed to the
    underlying image freeing up the space.

Enjoy.

Jirka