Michal Privoznik
c2bc419131
https://bugzilla.redhat.com/show_bug.cgi?id=1623389 If a device is detached twice from the same domain the following race condition may happen: 1) The first DetachDevice() call will issue "device_del" on qemu monitor, but since the DEVICE_DELETED event did not arrive in time, the API ends claiming "Device detach request sent successfully". 2) The second DetachDevice() therefore still find the device in the domain and thus proceeds to detaching it again. It calls EnterMonitor() and qemuMonitorSend() trying to issue "device_del" command again. This gets both domain lock and monitor lock released. 3) At this point, qemu sends us the DEVICE_DELETED event which is going to be handled by the event loop which ends up calling qemuDomainSignalDeviceRemoval() to determine who is going to remove the device from domain definition. Whether it is the caller that marked the device for removal or whether it is going to be the event processing thread. 4) Because the device was marked for removal, qemuDomainSignalDeviceRemoval() returns true, which means the event is to be processed by the thread that has marked the device for removal (and is currently still trying to issue "device_del" command) 5) The thread finally issues the "device_del" command, which fails (obviously) and therefore it calls qemuDomainResetDeviceRemoval() to reset the device marking and quits immediately after, NOT removing any device from the domain definition. At this point, the device is still present in the domain definition but doesn't exist in qemu anymore. Worse, there is no way to remove it from the domain definition. Solution is to note down that we've seen the event and if the second "device_del" fails, not take it as a failure but carry on with the usual execution. Signed-off-by: Michal Privoznik <mprivozn@redhat.com> ACKed-by: Peter Krempa <pkrempa@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 2.1 (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. For example, to build in a manner that is suitable for installing as root, use:
$ ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
$ make
$ sudo make install
While to build & install as an unprivileged user
$ ./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: