2a51ff7b40
Connecting a tap device to an Open vSwitch is done by adding a "port"
to the switch with the ovs-vsctl "add-port" command. The port will
have the same name as the tap device, but it is a separate entity, and
can survive beyond the destruction of the tap device (although under
normal circumstances the port will be deleted around the same time the
tap device is deleted).
This makes it possible for a port of a particular name to already
exist at the time libvirt calls ovs-vsctl to add that port. The
original commit of Open vSwitch support (commit df81004632, libvirt
0.9.10, Feb. 2012) used the "--may-exist" option to the add-port
command to indicate that a port of the desired name might already
exist, and that it was okay to simply re-use this port (rather than
failing with an error message).
Then in commit 33445ce8446d9 (libvirt 1.2.7, April 2014) the command
was changed to use "--if-exists del-port blah" instead of
"--may-exist". The reason given was that there was a bug in OVS where
a stale port would be unusable even though it still existed; the
workaround was to forcibly delete any existing port prior to adding
the new port (of the same name). This is the ovs-vsctl command still
in use by libvirt today.
It recently came up in the discussion of a bug concerning guest packet
loss during OpenStack upgrades (https://bugzilla.redhat.com/1963164)
that the bug in OVS that necessitated the del-port workaround was
fixed quite a long time ago (August 2015):
e21c6643a0
thus rendering the workaround in libvirt unnecessary. The assertion in
that discussion is that this workaround is now the cause of the packet
loss being experienced during OpenStack upgrades. I'm not convinced
this is the case, but it does appear that there is no reason to carry
this workaround in libvirt any longer, so this patch reverts the code
back to the original behavior (using "--may-exist" instead of
"--if-exists del-port").
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
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:
- 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: