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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.
f5418b427e
When firewalld is stopped, it removes *all* iptables rules and chains, including those added by libvirt. Since restarting firewalld means stopping and then starting it, any time it is restarted, libvirt needs to recreate all the private iptables chains it uses, along with all the rules it adds. We already have code in place to call networkReloadFirewallRules() any time we're notified of a firewalld start, and networkReloadFirewallRules() will call networkPreReloadFirewallRules(), which calls networkSetupPrivateChains(); unfortunately that last call is called using virOnce(), meaning that it will only be called the first time through networkPreReloadFirewallRules() after libvirtd starts - so of course when firewalld is later restarted, the call to networkSetupPrivateChains() is skipped. The neat and tidy way to fix this would be if there was a standard way to reset a pthread_once_t object so that the next time virOnce was called, it would think the function hadn't been called, and call it again. Unfortunately, there isn't any official way of doing that (we *could* just fill it with 0 and hope for the best, but that doesn't seem very safe. So instead, this patch just adds a static variable called chainInitDone, which is set to true after networkSetupPrivateChains() is called for the first time, and then during calls to networkPreReloadFirewallRules(), if chainInitDone is set, we call networkSetupPrivateChains() directly instead of via virOnce(). It may seem unsafe to directly call a function that is meant to be called only once, but I think in this case we're safe - there's nothing in the function that is inherently "once only" - it doesn't initialize anything that can't safely be re-initialized (as long as two threads don't try to do it at the same time), and it only happens when responding to a dbus message that firewalld has been started (and I don't think it's possible for us to be processing two of those at once), and even then only if the initial call to the function has already been completed (so we're safe if we receive a firewalld restart call at a time when we haven't yet called it, or even if another thread is already in the process of executing it. The only problematic bit I can think of is if another thread is in the process of adding an iptable rule at the time we're executing this function, but 1) none of those threads will be trying to add chains, and 2) if there was a concurrency problem with other threads adding iptables rules while firewalld was being restarted, it would still be a problem even without this change. This is yet another patch that fixes an occurrence of this error: COMMAND_FAILED: '/usr/sbin/iptables -w10 -w --table filter --insert LIBVIRT_INP --in-interface virbr0 --protocol tcp --destination-port 67 --jump ACCEPT' failed: iptables: No chain/target/match by that name. In particular, this resolves: https://bugzilla.redhat.com/1813830 Signed-off-by: Laine Stump <laine@redhat.com> Reviewed-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
============
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:
https://libvirt.org/contact.html