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The ATTRIBUTE_NONNULL(m) macro normally resolves to the gcc builtin __attribute__((__nonnull__(m))). The effect of this in gcc is unfortunately only to make gcc believe that "m" can never possibly be NULL, *not* to add in any checks to guarantee that it isn't ever NULL (i.e. it is an optimization aid, *not* something to verify code correctness.) - see the following gcc bug report for more details: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17308 Static source analyzers such as clang and coverity apparently can use ATTRIBUTE_NONNULL(), though, to detect dead code (in the case that the arg really is guaranteed non-NULL), as well as situations where an obviously NULL arg is given to the function. https://bugzilla.redhat.com/show_bug.cgi?id=815270 is a good example of a bug caused by erroneous application of ATTRIBUTE_NONNULL(). Several people spent a long time staring at this code and not finding the problem, because the problem wasn't in the function itself, but in the prototype that specified ATTRIBUTE_NONNULL() for an arg that actually *wasn't* always non-NULL, and caused a segv when dereferenced (even though the code that dereferenced the pointer was inside an if() that checked for a NULL pointer, that code was optimized out by gcc). There may be some very small gain to be had from the optimizations that can be inferred from ATTRIBUTE_NONNULL(), but it seems safer to err on the side of generating code that behaves as expected, while turning on the attribute for static analyzers.
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