a60ee91400
Back in July 2010, commit 6ea90b84 (meant to resolve https://bugzilla.redhat.com/571991 ) added code to set the MAC address of any tap device to the associated guest interface's MAC, but with the first byte replaced with 0xFE. This was done in order to assure that 1) the tap MAC and guest interface MAC were different (otherwise L2 forwarding through the tap would not work, and the kernel would repeatedly issue a warning stating as much). 2) any bridge device that had one of these taps attached would *not* take on the MAC of the tap (leading to network instability as guests started and stopped) A couple years later, https://bugzilla.redhat.com/798467 was filed, complaining that a user could configure a tap-based guest interface to have a MAC address that itself had a first byte of 0xFE, silently (other than the kernel warning messages) resulting in a non-working configuration. This was fixed by commit 5d571045, which logged an error and failed the guest start / interface attach if the MAC's first byte was 0xFE. Although this restriction only reduces the potential pool of MAC addresses from 2^46 (last two bits of byte 1 must be set to 10) by 2^32 (still 4 orders of magnitude larger than the entire IPv4 address space), it also means that management software that autogenerates MAC addresses must have special code to avoid an 0xFE prefix. Now after 7 years, someone has noticed this restriction and requested that we remove it. So instead of failing when 0xFE is found as the first byte, this patch removes the restriction by just replacing the first byte in the tap device MAC with 0xFA if the first byte in the guest interface is 0xFE. 0xFA is the next-highest value that still has 10 as the lowest two bits, and still 2) meets the requirement of "tap MAC must be different from guest interface MAC", and 3) is high enough that there should never be an issue of the attached bridge device taking on the MAC of the tap. The result is that *any* MAC can be chosen by management software (although it would still not work correctly if a multicast MAC (lowest bit of first byte set to 1) was chosen), but that's a different issue). Signed-off-by: Laine Stump <laine@redhat.com> Reviewed-by: Michal Privoznik <mprivozn@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 2.0 (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: