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During post-copy migration (once it actually switches to post-copy mode) dirty memory pages are continued to be migrated iteratively, while the destination can explicitly request a specific page to be migrated before the iterative process gets to it (which happens when a guest wants to read a page that was not migrated yet). Without the postcopy-preempt capability enabled such pages need to wait until all other pages already queued are transferred. Enabling this capability will instruct the hypervisor to create a separate migration channel for explicitly requested pages so that they can preempt the queue. The only requirement for the feature to work is running a migration over a protocol that supports multiple connections. In other words, we can't pre-create the connection and pass its file descriptor to QEMU (i.e., using MIGRATION_DEST_CONNECT_SOCKET), but we have to let QEMU open the connections itself (using MIGRATION_DEST_SOCKET). This change is applied to all post-copy migrations even if postcopy-preempt is not supported to avoid making the code even uglier than it is now. There's no real difference between the two methods with modern QEMU (which can properly report connection failures) anyway. This capability is enabled for all post-copy migration as long as the capability is supported on both sides of migration. https://issues.redhat.com/browse/RHEL-7100 Signed-off-by: Jiri Denemark <jdenemar@redhat.com> Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Libvirt API for virtualization
Libvirt provides a portable, long term stable C API for managing the virtualization technologies provided by many operating systems. It includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER Hypervisor.
For some of these hypervisors, it provides a stateful management daemon which runs on the virtualization host allowing access to the API both by non-privileged local users and remote users.
Layered packages provide bindings of the libvirt C API into other languages including Python, Perl, PHP, Go, Java, OCaml, as well as mappings into object systems such as GObject, CIM and SNMP.
Further information about the libvirt project can be found on the website:
License
The libvirt C API is distributed under the terms of GNU Lesser General Public License, version 2.1 (or later). Some parts of the code that are not part of the C library may have the more restrictive GNU General Public License, version 2.0 (or later). See the files COPYING.LESSER and COPYING for full license terms & conditions.
Installation
Instructions on building and installing libvirt can be found on the website:
https://libvirt.org/compiling.html
Contributing
The libvirt project welcomes contributions in many ways. For most components the best way to contribute is to send patches to the primary development mailing list. Further guidance on this can be found on the website:
https://libvirt.org/contribute.html
Contact
The libvirt project has two primary mailing lists:
- users@lists.libvirt.org (for user discussions)
- devel@lists.libvirt.org (for development only)
Further details on contacting the project are available on the website: