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8.124. libvirt

Updated libvirt packages that fix numerous bugs and add various enhancements are now available for Red Hat Enterprise Linux 6.
The libvirt library is a C API for managing and interacting with the virtualization capabilities of Linux and other operating systems. In addition, libvirt provides tools for remote management of virtualized systems.

Bug Fixes

Previously, the logic behind using the virsh command with the --config option, which handles the virtual domain configuration, was incorrect. Consequently, block devices were attached to both the domain configuration and the running domain. Both the handling logic and relevant technical documentation have been fixed, and virsh with --config now behaves correctly, attaching the block device to the domain configuration only.
Prior to this update, the libvirt Python bindings for querying block job status could not distinguish between returning an error and no status available. As a consequence, the code that was polling for the completion of a block job had to deal with a Python exception, and could not distinguish it from an actual error. With this update, the bindings now successfully determine if there is no job and return an empty dictionary when that is the case. As a result, the bindings can be used more reliably when managing block jobs.
A previous update introduced an error where a SIG_SETMASK argument was incorrectly replaced by a SIG_BLOCK argument after the poll() system call. Consequently, the SIGCHLD signal could be permanently blocked, which caused signal masks not to return to their original values and defunct processes to be generated. With this update, the original signal masks are restored as intended, and poll() now functions correctly.
When hot unplugging a virtual CPU (vCPU) from a guest using libvirt, the current Red Hat Enterprise Linux QEMU implementation does not remove the corresponding vCPU thread. Consequently, libvirt did not detect the vCPU count correctly after a vCPU was hot unplugged, and it was not possible to hot plug a vCPU after a hot unplug. In this update, information from QEMU is used to filter out inactive vCPU threads of disabled vCPUs, which allows libvirt to perform the hot plug.
Prior to this update, the condition that checks whether QEMU successfully attached a new disk to a guest contained a typographical error. Due to the error, the libvirtd daemon terminated unexpectedly if the monitor command was unsuccessful: for example, when a virtual machine failed or when attaching a guest disk drive was interrupted. In this update, the error has been corrected, and libvirtd no longer crashes in the described circumstances.
The libvirt library has limits on Remote Procedure Call (RPC) messages to prevent Denial of Service (DoS) attacks. Previously, however, the domain XML file could fail this limit test when it was encoded into an RPC message and sent to the target machine during migration. As a consequence, the migration failed even though the domain XML format was valid. To fix this bug, the RPC message limits have been increased, and the migration now succeeds, while libvirt stays resistant to DoS attacks.
Due to a regression caused by a prior bug fix, attempting to perform a block copy while another block copy was already in progress could cause libvirt to reset the information about the block copy in progress. As a consequence, libvirt failed to recognize if the copied file format was raw, and performed a redundant format probe on the guest disk. This update fixes the regression and libvirt no longer performs incorrect format probes.
The UUID (Universally Unique Identifier) is a string of characters which represents the virtual guest. Displaying the UUID on a screen requires correct APIs to present the strings in a user-readable format. Previously, printing unformatted UUID data caused exceptions or incorrectly formatted output. For Python scripts, exceptions that were not handled could cause unexpected failures. For other logging methods or visual displays, the characters in the output were jumbled. With this update, the UUID strings are properly formatted and printing them no longer causes unexpected exceptions or jumbled characters on output.
When receiving NUMA (Non-Uniform Memory Access) placement advice, the current memory was used for the amount parameter. As a consequence, domain placement was not as precise as it could have been if the current memory changed for the live domain. With this update, the advice is queried with the maximum memory as the amount parameter, and the advised placement now fixes the domain even when the current memory changes for the live domain.
Previously, libvirt reported success of the device_del command even when the device was not successfully detached. With this update, libvirt always verifies whether device_del succeeded, and when the command fails, libvirt reports it accordingly.
Prior to this update, using the virsh pool-refresh command incorrectly caused libvirt to remove a storage pool if a storage volume was removed while the command was being processed. As a consequence, the storage pool became inactive, even though the NFS directory was mounted. With this update, refreshing a storage pool no longer removes a volume from it. As a result, libvirt does not cause the storage pool to become inactive.


A new pvpanic virtual device can now be attached to the virtualization stack and a guest panic can cause libvirt to send a notification event to management applications.
This update adds support for the following Broadwell microarchitecture processors' instructions: ADCX, ADOX, RDSEED, and PREFETCHW. This improves the overall performance of KVM.
Users of libvirt are advised to upgrade to these updated packages, which fix these bugs and add these enhancements. After installing the updated packages, libvirtd will be restarted automatically.