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Libvirt native C API and daemons
f9f5ab5718
The virNumaNodeIsAvailable function is stubbed out when building
without libnuma, such that it just returns a constant value. When
CLang is optimizing, it does inter-procedural analysis across
function calls. When it sees that the call to virNumaNodeIsAvailable
returns a fixed constant, it elides the conditional check for errors
in the callers such as virNumaNodesetIsAvailable.
This is a valid optimization as the C standard declares that there
must only be one implementation of each function in a binary. This
is normally the case, but ELF allows for function overrides when
linking or at runtime with LD_PRELOAD, which is technically outside
the mandated C language behaviour.
So while CLang's optimization works fine at runtime, it breaks in our
test suite which aims to mock the virNumaNodeIsAvailable function so
that it has specific semantics regardless of whether libnuma is built
or not. The return value check optimization though means our mock
override won't have the right effect. The mock will be invoked, but
its return value is not used.
Potentially the same problem could be exhibited with GCC if certain
combinations of optimizations are enabled, though thus far we've
not seen it.
To be robust on both CLang and GCC we need to make it more explicit
that we want to be able to replace functions and thus optimization
of calls must be limited. Currently we rely on 'noinline' which
does successfully prevent inlining of the function, but it cannot
stop the eliding of checks based on the constant return value.
Thus we need a bigger hammer.
There are a couple of options to disable this optimization:
* Annotate a symbol as 'weak'. This is tells the compiler
that the symbol is intended to be overridable at linktime
or runtime, and thus it will avoid doing inter-procedural
analysis for optimizations. This was tried previously but
have to be reverted as it had unintended consequences
when linking .a files into our final .so, resulting in all
the weak symbol impls being lost. See commit
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| docs | ||
| examples | ||
| include | ||
| po | ||
| scripts | ||
| src | ||
| tests | ||
| tools | ||
| .ctags | ||
| .dir-locals.el | ||
| .editorconfig | ||
| .gitattributes | ||
| .gitignore | ||
| .gitlab-ci.yml | ||
| .gitmodules | ||
| .gitpublish | ||
| .mailmap | ||
| AUTHORS.rst.in | ||
| config.h | ||
| configmake.h.in | ||
| CONTRIBUTING.rst | ||
| COPYING | ||
| COPYING.LESSER | ||
| gitdm.config | ||
| libvirt-admin.pc.in | ||
| libvirt-lxc.pc.in | ||
| libvirt-qemu.pc.in | ||
| libvirt.pc.in | ||
| libvirt.spec.in | ||
| meson_options.txt | ||
| meson.build | ||
| NEWS.rst | ||
| README.rst | ||
| run.in | ||
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==============================
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
============
Instructions on building and installing libvirt can be found on the website:
https://libvirt.org/compiling.html
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