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Before libvirt sets the MAC address of the physdev (the physical ethernet device) linked to a macvtap passthrough device, it always saves the previous MAC address to restore when the guest is finished (following a "leave nothing behind" policy). For a long time it accomplished the save/restore with a combination of ioctl(SIOCGIFHWADDR) and ioctl(SIOCSIFHWADDR), but in commit cbfe38c (first in libvirt 1.2.15) this was changed to use netlink RTM_GETLINK and RTM_SETLINK commands sent to the Physical Function (PF) of any device that was detected to be a Virtual Function (VF). We later found out that this caused problems with any devices using the Cisco enic driver (e.g. vmfex cards) because the enic driver hasn't implemented the function that is called to gather the information in the IFLA_VFINFO_LIST attribute of RTM_GETLINK (ndo_get_vf_config() for those keeping score), so we would never get back a useful response. In an ideal world, all drivers would implement all functions, but it turns out that in this case we can work around this omission without any bad side effects - since all macvtap passthrough <interface> definitions pointing to a physdev that uses the enic driver *must* have a <virtualport type='802.1Qbh'>, and since no other type of ethernet devices use 802.1Qbh, libvirt can change its behavior in this case to use the old-style. ioctl(SIOC[GS]IFHWADDR). That's what this patch does. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1257004
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>