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The udev monitor thread "udevEventHandleThread()" will lag the
actual/real view of devices in sysfs as it serially processes udev
monitor events. So for instance if you were to run the following cmd
to create a new veth pair and rename one of the veth endpoints
you might see the following monitor events and real world that looks like
time
| create v0 sysfs entry
wake udevEventHandleThread | create v1 sysfs entry
udev_monitor_receive_device(v1-add) | move v0 sysfs to v2
udevHandleOneDevice(v1) |
udev_monitor_receive_device(v0-add) |
udevHandleOneDevice(v0) | <--- error msgs in virNetDevGetLinkInfo()
udev_monitor_receive_device(v2-move) | as v0 no longer exists
udevHandleOneDevice(v2) |
\/
As you can see the changes in sysfs can take place well before we get
to act on the events in the udevEventHandleThread(), so by the time we
get around to processing the v0 add event, the sysfs entry has been
moved to v2.
To work around this we check if the sysfs entry is valid before
attempting to read it and don't bother trying to read link info if
not. This is safe since we will never read sysfs entries earlier than
it existing, ie. if the entry is not there it has either been removed
in the time since we enumerated the device or something bigger is
busted, in either case, no sysfs entry, no link info. In the case
described above we will eventually get the link info as we work
through the queue of monitor events and get to the 'move' event.
https://bugzilla.redhat.com/show_bug.cgi?id=1557902
Signed-off-by: Mark Asselstine <mark.asselstine@windriver.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
.. image:: https://travis-ci.org/libvirt/libvirt.svg
:target: https://travis-ci.org/libvirt/libvirt
:alt: Travis CI Build Status
.. image:: https://bestpractices.coreinfrastructure.org/projects/355/badge
:target: https://bestpractices.coreinfrastructure.org/projects/355
:alt: CII Best Practices
==============================
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