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The nwfilter update lock is historically acquired by the virt drivers in order to achieve serialization between nwfilter define/undefine, and instantiation/teardown of filters. When running in the modular daemons, however, the mutex that the virt drivers are locking is in a completely different process from the mutex that the nwfilter driver is locking. Serialization is lost and thus call from the virt driver to virNWFilterBindingCreateXML can deadlock with a concurrent call to the virNWFilterDefineXML method. The solution is surprisingly easy, the update lock simply needs acquiring in the virNWFilterBindingCreateXML method and virNWFilterBindingUndefine method instead of in the virt drivers. The only semantic difference here is that when a virtual machine has multiple NICs, the instantiation and teardown of filters is no longer serialized for the whole VM, but rather for each NIC. This should not be a problem since the virt drivers already need to cope with tearing down a partially created VM where only some of the NICs are setup. Reviewed-by: Laine Stump <laine@redhat.com> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
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==============================
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:
https://libvirt.org
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:
https://libvirt.org/contact.html