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The QEMU driver uses the <teaming type='persistent|transient' persistent='blah'/> element to setup a "failover" pair of devices - the persistent device must be a virtio emulated NIC, with the only extra configuration being the addition of ",failover=on" to the device commandline, and the transient device must be a hostdev NIC (<interface type='hostdev'> or <interface type='network'> with a network that is a pool of SRIOV VFs) where the extra configuration is the addition of ",failover_pair_id=$aliasOfVirtio" to the device commandline. These new options are supported in QEMU 4.2.0 and later. Extra qemu-specific validation is added to ensure that the device type/model is appropriate and that the qemu binary supports these commandline options. The result of this will be: 1) The virtio device presented to the guest will have an extra bit set in its PCI capabilities indicating that it can be used as a failover backup device. The virtio guest driver will need to be equipped to do something with this information - this is included in the Linux virtio-net driver in kernel 4.18 and above (and also backported to some older distro kernels). Unfortunately there is no way for libvirt to learn whether or not the guest driver supports failover - if it doesn't then the extra PCI capability will be ignored and the guest OS will just see two independent devices. (NB: the current virtio guest driver also requires that the MAC addresses of the two NICs match in order to pair them into a bond). 2) When a migration is requested, QEMu will automatically unplug the transient/hostdev NIC from the guest on the source host before starting migration, and automatically re-plug a similar device after restarting the guest CPUs on the destination host. While the transient NIC is unplugged, all network traffic will go through the persistent/virtio device, but when the hostdev NIC is plugged in, it will get all the traffic. This means that in normal circumstances the guest gets the performance advantage of vfio-assigned "real hardware" networking, but it can still be migrated with the only downside being a performance penalty (due to using an emulated NIC) during the migration. Signed-off-by: Laine Stump <laine@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@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
Libvirt uses the GNU Autotools build system, so in general can be built and installed with the usual commands, however, we mandate to have the build directory different than the source directory. For example, to build in a manner that is suitable for installing as root, use:
$ mkdir build && cd build
$ ../configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
$ make
$ sudo make install
While to build & install as an unprivileged user
$ mkdir build && cd build
$ ../configure --prefix=$HOME/usr
$ make
$ make install
The libvirt code relies on a large number of 3rd party libraries. These will
be detected during execution of the configure script and a summary printed
which lists any missing (optional) dependencies.
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:
- libvirt-users@redhat.com (for user discussions)
- libvir-list@redhat.com (for development only)
Further details on contacting the project are available on the website: