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Despite the comment stating virNetClientIncomingEvent handler should never be called with either client->haveTheBuck or client->wantClose set, there is a sequence of events that may lead to both booleans being true when virNetClientIncomingEvent is called. However, when that happens, we must not immediately close the socket as there are other threads waiting for the buck and they would cause SIGSEGV once they are woken up after the socket was closed. Another thing is we should clear all remaining calls in the queue after closing the socket. The situation that can lead to the crash involves three threads, one of them running event loop and the other two calling libvirt APIs. The event loop thread detects an event on client->sock and calls virNetClientIncomingEvent handler. But before the handler gets a chance to lock client, the other two threads (T1 and T2) start calling some APIs. T1 gets the buck and detects EOF on client->sock while processing its RPC call. Since T2 is waiting for its own call, T1 passes the buck on to it and unlocks client. But before T2 gets the signal, the event loop thread wakes up, does its job and closes client->sock. The crash happens when T2 actually wakes up and tries to do its job using a closed client->sock.
libvirt library code README
===========================
The directory provides the bulk of the libvirt codebase. Everything
except for the libvirtd daemon and client tools. The build uses a
large number of libtool convenience libraries - one for each child
directory, and then links them together for the final libvirt.so,
although some bits get linked directly to libvirtd daemon instead.
The files directly in this directory are supporting the public API
entry points & data structures.
There are two core shared modules to be aware of:
* util/ - a collection of shared APIs that can be used by any
code. This directory is always in the include path
for all things built
* conf/ - APIs for parsing / manipulating all the official XML
files used by the public API. This directory is only
in the include path for driver implementation modules
* vmx/ - VMware VMX config handling (used by esx/ and vmware/)
Then there are the hypervisor implementations:
* esx/ - VMware ESX and GSX support using vSphere API over SOAP
* hyperv/ - Microsoft Hyper-V support using WinRM
* lxc/ - Linux Native Containers
* openvz/ - OpenVZ containers using cli tools
* phyp/ - IBM Power Hypervisor using CLI tools over SSH
* qemu/ - QEMU / KVM using qemu CLI/monitor
* remote/ - Generic libvirt native RPC client
* test/ - A "mock" driver for testing
* uml/ - User Mode Linux
* vbox/ - Virtual Box using native API
* vmware/ - VMware Workstation and Player using the vmrun tool
* xen/ - Xen using hypercalls, XenD SEXPR & XenStore
* xenapi/ - Xen using libxenserver
Finally some secondary drivers that are shared for several HVs.
Currently these are used by LXC, OpenVZ, QEMU, UML and Xen drivers.
The ESX, Hyper-V, Power Hypervisor, Remote, Test & VirtualBox drivers all
implement the secondary drivers directly
* cpu/ - CPU feature management
* interface/ - Host network interface management
* network/ - Virtual NAT networking
* nwfilter/ - Network traffic filtering rules
* node_device/ - Host device enumeration
* secret/ - Secret management
* security/ - Mandatory access control drivers
* storage/ - Storage management drivers
Since both the hypervisor and secondary drivers can be built as
dlopen()able modules, it is *FORBIDDEN* to have build dependencies
between these directories. Drivers are only allowed to depend on
the public API, and the internal APIs in the util/ and conf/
directories